I never even saw one until I reached college. There are a few cases where you need it in order to avoid ambiguity, but in general it's optional. You just need to have consistency.

If you're writing professionally though; that's going to be different. Each publication will have a style guide that will tell you about things like that.

The Youtube page had some good examples such as: I invited the strippers, Adolf and Stalin. That's ambiguous and you may want to add an Oxford comma for clarity. It could be either the names of the strippers or two additional invitations. But, if you say "I invited the strippers, Adolf and Stalin to the party," that's no longer ambiguous, you've invited at least 4 people to the party.

For the most part, the rules change over time and really the aim is clarity and reliability.

Personally, I'm usually too lazy to bother grammar checking forum posts as forum posts are informal register.
A dangling participle is something that's going to depend more on context than if the sentence was constructed with more care. In practice, these things are much more problematic in isolation. If you've got sentences with dangled participles in the middle of a conversation you'll use the context to guess the correct one or you'll ask. In most cases though you'll know which one it is.

In a more formal register, you might not want to dangle the participles, but that's a register thing rather than a grammar thing, it wouldn't be any less grammatical to use the contraction can't in a formal paper, but it's frowned on.