9 - 5, if I'm not getting paid enough to make a living, I can't spend too long on a job regardless if they are friends (family is different). I work for myself, my friends bosses would not ask them to work a day unpaid.
I have found that if I've done free work for friends, people assume that what I do has little professional value. If I send out the message that my time and service is worthless, friends will think nothing of taking more of it in revisions and tweaks.
I planned a shop for a friend for no charge, because at the time he was short of cash, but he still had to pay his contractors (all friends) who needed my plans to work off. At the end of the day I had made a loss on printing plans etc. But if somebody walked into his shop, they wouldn't get free groceries however well they knew him.
I think you answer your own question in the title of your thread. If you love your job, you have to make money, or you can't afford to do it.