While you don't get rich working on a per-hour basis, you don't lose your butt on jobs either. This can really help on jobs where it's hard to estimate the time required. Or when you're unsure of materials required and can bill based on time and materials.
It's important to have differential rates, though, to account for different equipment used, etc. For example, we charge $65/day for a chipper whether it's used or not. Of course, the time spent chipping is above and beyond that, but fees help bump up the price and into profit.
Another thing is a minimum charge per job. For us, it's $225. No matter how small the task, it's $225 for us to show up with a truck/crew/chipper. Usually, this isn't a problem, but for really small jobs, we propose doing more work than just what may have been requested. For example, "we can take that limb off, but it'll be $225. As part of that, we can go ahead and prune the rest of the tree" ...... etc.