Ive been dry firing my pcps every week for over 25 years especially my regulated guns, if anything its good for them.
Imagine leaving a car in a garage for years what happens to the tyres, they crack because rubber will go hard when not exercised, same with the coil springs an old car might crack a spring if not used often at the first speed bump it hits.
Same with pcps when you fire them regularly it keeps the rubber supple, imagine all the o rings in the gun flexing as the pressure equalises, it certainly kept mine in good order, I put some shots over chrono with my mk2 rapid the other day its not had a pellet through it in nearly a year the results were just 2 fps variation over 10 shots, I put that down to regularly dry firing it.
Every gun I have is exceptionally accurate, I dont own anything average, I put that not only down to the barrel and ammo but down to regular use, like any well oiled machine gets slicker when bedded in, all bearing surfaces bed in regular use keeps them free from getting sticky or forming any internal corrosion, any oil or grease can kind of coagulate if not used regularly, Ive serviced guns that were filled with grease from the factory and it goes thick and sticky without use, anyone who has pulled for example a hw100 apart will vouch for that, a regularly used one will often have a more jellied type of grease than one which hasnt been used often, and so the first thing some owners tend to do is degrease them, as viscosity also changes with temperature therefore consistency, some people run them dry but personally I very lightly lube them, and after I service them I advise regular use even if thats dry firing regularly, and they tend to get better and better, and go longer between services.