I buy tear the moment i get 750 gold.. It is a must have for ME, considering how poke and gank heavy is bot lane this season. Without tear my sustain is non-existent. Also as first buy i stack it pretty, pretty fast. I start stacking it the moment i purchase it, while leaving fountain i spam spells, while running to lane i spam Q .. I never run out of mana the moment i buy it. Also if the game lasts long enough or if I'm ahead, the upgrade saved me 102952 times with the shield, also the AP it provides makes her spells and heals even stronger- so basically never ending - stronger heals.
Combined with ardent and redemption - my mana is never ending. I never used dangerous game, because every gold piece helps Sona, she is a very item reliant support, in order to get CDR and other stats too.
I genuinely can't understand Sona players who don't get it. Without it, heal, Q, speed spam at mid/late game is impossible to do. But I also can't blame others for doing what works for them. Sona heals are actually very potent with the right combination of items + tear..I typically do Soraka levels of healing in the long run, considering how safely, often and without 'almost' any cost i can use them. If it's end game, I even sell my boots for Spirit Visage, making me extremely tanky , my self healing trough the roof and act as a second tank in a sense. Too bad her early game is so abysmal.
Yesterday We did a 5 minutes non-stop siege and I spammed heal + Q like crazy, until we finally won.. My team couldn't even believe how long we've lasted with my never ending heals and shields. Without tear it wouldn't be possible and the enemies could have a chance to recover and turn around the game.