Could be useful...depends on how rolling and broken up the fields are in that area. If it's a lot of square fields w/ not many waterways or terraces they're not real important or needed. 

If you're in an area with a lot of curved edges, waterways, terraces, etc then they're super helpful for a lot of things. 

Then comes the issue of charging....if you charge per acre you're over charging for the big flat simple ones. And getting screwed on the little odd stuff. Do you charge per hour? Just have to find a sweet spot and try it

Edit to add: this is assuming RTK accuracy. Don't bother with WAAS or something else that drifts over time or you're wasting your time