Grass is OK if smooth; it is what you find in the grass that might be a problem.
Potholes for example. I had a pothole prop strike when new; £20,000.... And the airport washes its hands of liability. So
you, the pilot, need to be vigilant. If in any doubt, get out and walk the taxi route - even if there is a queue behind you. They won't be footing your prop strike bill
I tend to not do grass in the winter because the plane gets covered in muck, and due to the rut problem below.
Another thing is to get hard parking if possible. A lot of grass runway airfields have a hard parking area. I had to get my plane pulled out (from a rut) with a vehicle more than once, and most fire crews doing this will just do it by the nosewheel
so ripping off the engine mount. One needs two ropes, pulling on the main wheels.
Otherwise, grass is fine. Taxi with the yoke all the way back to relieve the nosewheel pressure, and do a "soft field" take off whenever possible. I never did those in the JAA PPL; only the FAA one teaches them, it seems.
However, hard runways can be as bad. I know of some (Elstree and Spanhoe being the worst) which are covered in stones, and the users there must be getting a high rate of nicks. These translate into early prop overhauls, or unneccesarily early blade scrappings during scheduled prop overhauls, and that is 4 digits. The technique is to avoid high power slow speed taxi over areas where there are most stones; build up speed before these and then cut the revs. I don't know why somebody doesn't get a broom... at least with grass you don't get this problem.
Having said that, the worst runway I have ever been to was Heywood Farm - a scary experience I am not repeating. Followed by a £200 cleanup job.