I think that the wall is there for a reason and shouldn't be broken if it is a serious story. Explain things later if you think that the readers might not understand what is going on. If it is a comedy like the Emperor's New Groove, it is different, but even then I think that it interrupts the story if dome badly or too often.
I think it works better in TV shows but in fanfics, I am usually not a fan. It has never been done well in my opinion in the fanfics I've read.
It does work better in movies and cartoons, but it is often awkward in fanfics, mostly because it interrupts the flow of the story. Tastefully done, it can be very funny.
I never break the forth wall in any of my stories. It's there for a reason. I might lean on it every now and then, such as when Niles comments on Lux's tendency to win because it's like he's the main character or something. Other than those instances, I don't enjoy wall breaking unless it's a comedy or Disgaea.
I'm not sure if I have ever seen fourth wall breaking done well in a fanfic. I've seen it done well in some books though, like Lemony Snicket or Philip Ardagh...although in those cases the author is a character in their own right.
In my opinion, the fourth wall is a thing that you should not break, tap at, or actually, even attempt to touch. It ends up annoying me if the fourth wall is broken in the middle of a story I'm enjoying, as it interrupts the flow. Character talking to reader, eg 'My name is ---- and I'm sending this letter out' or whatever is fine. It can even be hilarious. But something like randomly breaking the wall in a story feels unnecessary to me. Sorry, I have really strong opinions... #MissingNo
Breaking the 4th wall to me is pretty stupid and a waste of time. However, if you can pull it off just right, it can actually be funny and clever. But most writers can't pull it off well, making the break look uncreative and awkward. 4th wall breaking can also be more acceptable in stories that have more of a "lighthearted" atmosphere, like my sister's fanfic. A 4th wall break there might seem okay, but in a darker story, don't even try it.
It depends how and when its used. If for comedic effect, im all for it. If the tone is very serious, then I see it as a cheap way to get some info out. I agree with the whole, it works better in cartoons idea as well.
Depends on the mood of story. For my JourneyFic, it's a lighthearted adventure so there are bound to be comedic moments. I would see it okay for me to poke at the wall of straight up break it in DSTM (aka my fanfic's codename if you've never read it) because it doesn't stray too far from the general mood of the story, as long as I do it well and not a cheap laugh or info dump. And if you're doing a straight-up comedy one-shot, I want to see that wall shattered! It's totally neccisary if you're doing a comedy story as you can get plenty of nice jokes and comments from fourth wall breaking. Now, let's say your story is exploring the darkest depths of something and there are tons of mature themes. Wouldn't it be weird to see a character suddenly become all cheery and say hello to the reader? That doesn't seem right. Basically, it's the tone of the story and if a fourth wall break is required.
Fourth wall breaking is great if done well, like the others said. Personally, if it's a narrative with a character telling a story (to the readers), I think it's not bad. But if it's misplaced it'll just ruin the mood.