It's beginning to get on my giddy goat.
Doing this is not the same as writing something in brackets
I also see people using it for no discernable reason whatsoever. Someone typing a normal paragraph suddenly starts crossing bits out at random.
It is for using when you say something that you know in your heart of hearts you really shouldn't but you want to say it anyway. Or for comic effect as in "I had half a packet of a couple of biscuits with my cup of tea".
IANBU so don't even talk to me.