when it comes to seo everyone talks about 50KB limits, then some talk about bandwidth packets. Now the question is that if i am creating an external css, javascript or image sprite what is the size limit? and why?

I think maybe this has something to do with internet connections at user side but what these packets has to do, i have no idea. As if there are limits and they provide advantage then i will split my css into two external files so that i could take advantage of these features.