Chalice of Harmony is, nowadays, only bought on AP mids, and then only sometimes. However, that is a lot less than it deserves. Just look at it: Cost is 890, you can sell it for 623 gold, which means that it actually costs you 267 gold if you sell it later in the game. Now imagine you are, for example, Malphite or Jayce against any top laner (AP would be most epic, but also buy it vs AD). You can forever on spam your Q to outlane and maybe even kill your lane opponent. It will end up at least giving you about 20-30 more cs (equals to about 400-600 gold), and might give you 1-2 more kills, equaling to 300-573 (if the enemy does not get a kill) more gold. There you got your gold, plus some more, back.

In short, it isn't only worth it on AP mids, but also on tops with mana, even against AD tops. In jungle I doubt it is worth it, maybe on a blue reliant jungler while the mid is also blue reliant, on support I don't think so. Only for example a Blitzcrank who is good at grabbing and, because of this, WILL earn the spent gold back through assists (58% of the killer's gold if he's the only assister), AD carries might be worth it on Varus, Graves or someone like that, who can outlane enemies with abilities if he doesn't have to worry about mana costs. But on tops it is worth it for sure.