Uses of [◯]{まる} symbol in Japanese typography

Question

What is [◯]{まる} symbol is typically used for?

The only usage I know of is the "correct" mark. But the dictionary says it is also used as a placeholder and for censorship, see ◯ and ◯◯.

Here are more detailed questions:

1. Are there any other uses?
2. Where can I typically see those?
3. Can it be used in grammar/spelling tests as a "fill the blank" for kanji?

Answer 1

I usually see ○○ when people refer to a series of related things with similar names. For example, here is an article about 危険な○○シリーズ, which is a series of comical video remixes that use the same song and are typically called 危険な[something].

Also on the Internet it can be used for self-censorship (often comical I think), like ち◯こ instead of ちんこ.

I've also (rarely) seen people using ●● instead, not sure if there is a difference.

Answer 2

I've seen it a lot on television shows to represent "something", probably like your placeholder you mentioned and also as censorship for words on the subtitle-like テロップ.

e.g. １００人に聞いた[この夏、◯◯をしたい！！]　TOP3ランキング！！！

e.g. う◯こ