I keep track of the hours as I write in black sharpie inside the back engine door oil/filter/ fuel filter changes by hours on the machine when done. I bought the machine right before a huge ice storm and had the lucky forethought to also buy a grapple bucket. It made money then for sure and also after a large tornado hit. I know I have had lots of people over the years want to borrow the machine.....uuuuh No. I told them I would make them a great rate for smaller low-risk jobs. Most pass .... When it broke down I had a neighbor call asking to borrow it and I said it was broke down but if he helped me fix it I would let him borrow it. He said he would get back to me....and he has never asked to borrow anything since.I too have thought about doing side work, but yeah, insurance etc.... Plus the fact my machine is a little older, i don't need it breaking down where i can't get it out.
I did about a weeks worth of work at my cousins place when he was lifting his house, that is the extent of outside work i have done.