No no no, this is not about actual hats and suitcases (who would write about those?); it’s about writing. I have always wondered what the big deal was about lower cases and upper cases. But I suppose they are used in different cases (pun not intended) not only restricted to grammar. For instance, in a chat with my friend on the internet, I would write something like this: hi there! how r u doing? do u hv time 2 chat? or something along those lines that does not follow English rules at all (my teacher would be horrified!). But on a blog or essay, I would have to be correct grammatically and spelling wise. Of course, it’s not easy, and I don’t always do it, but it’s a silent rule that everyone knows. Because it’s correct! You could be this correct on an e-mail, but, to me, it seems less personal and looks like you’re writing a proposal to a company.
I think it’s good to keep in mind grammatical rules, but let loose sometimes, as it’s fun!