Please keep in mind: you play an individual champion, not a position.
Especially in the support role I keep seeing this. Let's take blitzcrank as an example: the usual build being Coin item, sightstone, Boots, Micaelis, RG and an iceborns. And maybe one of that replaced by a Locket.
Whanever I see this I wonder: do you guys even have any clue how your champ works? Screw the standart tank support build, get a sightstone/gold item, boots and then cram your other slots full with stuff your champ is actually good with. In Blitzcranks case Mana and Ap. You have a passive that can be super strong... but most people just ignore it and think this puny 300 hp shield is all they can get from it.
Here, THIS is how you play Blitzcrank.
+ item depending on situation: You stomp, get
. Much enemy AD, get
, Much enemy AP get
. Eventually, swap iceborns for lichbane if you are REALLY stomping them.
"But the pros don't play it like that in LCS!"
Yeah, and these guys play in well trained teams that can perfectly react to a blitzcrank grab. But you're not in LCS. You are in SoloQ where you eventually have to carry four total morons. You don't just pull an enemy. You pull that guy and then kill that fucker with your ult. Also, thanks to the scaling on your ult, you're going to be a beats in teamfights and no mere hook bot.
Another example: Janna.
Why the fuck would you get a crucible on Janna? You already are the queen of disengage! Instead, go full ham like this:

Why you should do that? Simple. Go read up what your support keystone mastery does. A PERCENTAL increase of heals and shields. Meaning, it becomes more effecitce THE BIGGER THE INTIAL VALUE IS. And with some AP your E and R become total gamechanges. This applies to other casting supports as well, although some might rather pick
for an extra item like a hourglass or a ludens.