Alternating caps is capitalizing in the middle of a word or not capitalizing the beginning of the name, place, or sentence.

tHis iS an eXamPle Of alTenAtIon cApitALizatiOn.

This has everything to do with presentation. The flow of the words is broken with the capitalization and at some points break the words up into new words. It also gives the reader a harder time to read this as they go up and down the words like a roller coaster, which in the end annoys the reader and makes them skip your message or ignore all other messages from you.