Elite has the limits because they have so much traffic. If a site gets 100 hits a day, then they can afford to have each of those hits have a ton of shit on them.
But Elite gets way more than that, so they don't want to have to serve out all of that content when it is largely useless.
You don't want to limit the actual post content since that is what is new and good about your site - the creative mine share.
But avatars are a luxury, so there is no need to waste your bandwidth on those (hell, many sites don't allow them at all - those are usually sites with even more traffic than Elite, things more mainstream).
The signature, since it doesn't contain images, is more of an eyesore than it is an issue with bandwidth. That said, after a certain amount of text, then it approaches the size of an image, so it is worth limiting the size.
Technically, browsers cache images that are used over and over again, and therefore don't download them if it has seen them before. That setting can be changed, but it is on by default.
So if you have repeat visitors, they are only downloading what is new and not the avatars each time (hence why in order to see new avatars, you sometimes have to do a refresh outside of the cache).
Animated gifs have the data that each frame would hold, so they are that much larger than an individual frame would be (not sure off the top of my head if they do any compression where they only worry about the pixels that actually change) - the gif in general does something like this already, so perhaps it is built in, not sure.
I personally wish that the signatures were limited in visual size like they do on some sites, it just looks better. Prevent the huge letters and different colors.
Instead make everyone cool like me, since I am the standard to which everyone else should aspire.
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