Only for service - otherwise they get filled up after I shoot them and stored that way. Been into PCPs for over 10 years with no issues this way. Eventually all o-rings will need replaced, and a bit more pressure on them when static won't make much difference. In truth, the worst thing for them is the depressurization. As a result, once the rings are a few years old, I'll replace them all whenever I have to take that gun down for service. Some never really need touching - I have an Air Ranger from 2011 that holds fine on it's factory o-rings (knock on wood), but if it leaks they will all get replaced.