The posts that begin that way tend to be from followers of Islam. I expect there is some sort of function for proclaiming that they have properly performed their ritual ablutions and prayers. As a reader, and non-Muslim, what I interpret is a proclamation of faith and an assertion that they adhere to certain values.

It's all good for me--even if I don't truly need to be reminded every single post that they continue to be observant Muslims. :-) I trust them.