I keep seeing things pop up about it. Generaly i only get it on tank supports(so 
etc) and bard. with bard you are already roaming so why not throw down a few. also ive been told he works good as a tank so theres that.
remember to be nice, please no rank nazis.
Always. That's pretty much all the discussion needed.
A better question is
"how often do you buy wards (not just using your trinket) as the non-support?"
If you compare the answers to that with your question, the difference is startling. People expect a 0 cs support to sink their first 800 gold into vision when they aren't even willing to spend 75 gold every once in awhile throughout the entire game.
And people wonder why support mains get pissed off.
i buy sightstone every time i support no matter what. because if i didn't there would be no wards on the map and our jungle and neutral objectives would probably be littered with enemy wards.
Tank Supports: Mandatory - there's no reason not to buy it, HP and vision = win. AP Supports - completely depends on how the game is going. I've realistically only NOT bought sightstone as a support once and that was when my ADC was afk for the first 7 minutes and I ended up 4 and 0 bot lane with some great jungle help - otherwise I build sightstone, because having a scanner is mandatory for good supports so you can't rely on your trinket.
I don't buy sightstone anymore. In Bronze vision means jack shit. We could have the old ward system back where I can have the entire map lit up like a Christmas tree with every spare gold I could muster and the enemy Jungle would still get a double kill on bot lane while my team rages at me "wtf no wards? Noob support".
Always, I like keeping the two entry points and the river (or brush if there's a Leona or Blitz opposing us) lit up.
When i support, 99% its 
. My first back is generally Sheen or components + a pink and green, then i get sightstone on 2nd back.
I buy sights tone for every single support I play.
I always get it every time and can't imagine playing support without it.
100% of the games I go support I get one.
Truth to be told, I don't really care if someone wants to go Vladimir support or something like that, as long as they get the bare minimum and get Sightstone for vision control, they can do whatever they want.
The only case I can think of is something like an Annie-kind of Champion who's going 4/0 and basically carrying us, but then someone else should get the sighstone.
I always get it, and try to get it early. Vision at dragon and to protect from ganks is well worth the price tag. If I upgrade it or not is another story, unless it's late and I'm already full build
I always buy it. That might change if I could trust my team to upgrade their trinkets or ward appropriately, but that rarely happens in solo-queue. Sightstone also lets you get Oracle's Len for dewarding objectives and paths to arrange picks and rotations.
if you dont get it you just fucked your team and yourself. Vision is the single most important thing a support can provide for the team. You think its cool that you do damage in teamfights? so do i! really! But i like to plan those fights, and use the knowledge of where my enemy is to my advantage and chose the place of the teamfight because we know where they are! By all means, build your ap items or w/e. but do that AFTER you rush sightstone!!!
also take into account:
I build it on every support. They need it. Even if its just mid-game, you need that vision badly.
Always. Every single time. And a pink. And an upgraded red trinket.
Always ward, cause you might just be the only one warding. Nothing shuts up a teammate who yells at you for having low vision like "Well, all of the wards I can possibly place are already out, but I see you haven't even upgraded your yellow trinket yet, so..."
There is no reason to not buy it.
It will save you more gold as the game goes than anything else. (While you can argue gold generating items can gain you more, they also cost more, netting you less gold).
Don't bother bringing up the upgraded yellow trinket. You wont in a vision war with 2 charges. And you'll have to spend more gold on wards before level 9. Sightstone is easily gotten before level 6. Top it off getting red trinket brings in even more gold.
Edit: Now if you asked about Ruby Sightstone. I'd respond "When I'm rolling in so much gold I wonder why i didn't build damage."
Well, after a six game losing streak I'm starting to question its usefulness at low MMRs. I think one thing I'll enjoy a lot more about playing support when I've worked my way up higher is players who actually use vision to their advantage and try to stay one step ahead of enemy movements. Where I'm at though most other players don't even buy wards probably because they don't understand what they're for.
If the rest of the team upgrades their yellows post nine, you can probably get away with not getting a sightstone. I generally buy one, however it isn't always my first priority.
EVERY. SINGLE. GAME.
Unless the support gets super fed(or off-meta (or really off-meta)) then everyone upgrades trinkets and doesn't bother with denying vision.
For any support, tanks or not, Sightstone is always a first buy. Leaving as a last minute item is seriously risky & detrimental, as you get ganked for very low vision & losing multiple drag vision makes last minute warding more invaluable.
I get it if my ADC isn't kalista and/or nobody else is buying wards, especially if I can sacrifice one of my item slots for it (eg on Janna)
idk how else you're going to get vision, the trinket takes too long to charge.
Who needs vision if you have a minimap? Just pay attention to it.
Who said never?
Only if the game is going good because if it's going bad we usually cant stop drag/baron. I also dont if there is a Teemo on our team
I buy sightstone on every support ever. It's free wards, it pays for itself, and is honestly too good not to get. Plus if you really want to save money, you can then upgrade your trinket to either the red trinket, or the pink ward trinket.
