The Romans used all caps but then a bunch of liberals got all over their case for wasting stone and hide and killing a lot of sheep unnecessarily -- someone figured that if only a lower case size were put in use, it would save the lives of 7,321 sheep a year in government scrolls alone!!! Sooner or later one of the politicians decided to do something to win the youth contingent and forwarded the law to the Senate.

Now, however, this is not an excuse; electrons are in  near-infinite supply, and the reason for going tot he trouble of using upper AND lower case is flexibility of meaning and as a courtesy to your readers. 'Course if your attitude is 'fockken leddum figgerid out!' thern there really is no reason for you to notice conventions of writing, unless you want to be understood!