While playing GTA4, I sometimes run across these blue person icons that the game refers to as a "friend" which is like a small side mission. Sometimes I accidentally walk into them without noticing and just complete them because that seems like the easiest thing to do.
Do these friend side missions contribute anything t the overall story line, or are they just there to be there? Is there a set list of friend missions you can do? Do they unlock something for completing all of them? Overall, is there any real benefit to me for completing them?
P.S. I'm not talking about your friends that you can call on your phone.