Some years ago I did so part time instructing at a small grass airfield that welcomed visitors on PPR only. The idea was to gain some idea of the visitors experience before commiting, effectivly a screening process. It's amazing how many PPLs who learned at a large airfield have serious trouble with 600m of wet grass. Every year there would be an aircraft in the hedge.
There are other hazards with grass airfields in winter. Nose wheel aircraft on water logged ground isn't a good idea if you don't know in advance. If PPR is asked there's a reason, please comply.