Welcome to the wonderful world of not knowing what the hell most of us SI for. There are various reasons. I know for me, I don't know why I do/did it to this day. I was too afraid to talk to my T about it, so I never got to figure it out. If you're curious, maybe you should ask your T? Or if you don't have one...maybe find one, if you want.

Sorry I don't have a better answer for you.