If the recording is an on going project and they are on the day hourly rate (based on what an hour would be as part of a full day booking which I call the project rate), I let everyone use what they want from the studio for free.
If it's one of those bookings that that band tells me they can record an album in a few hours because they are really rehearsed and the songs are only 3 minutes long, and they are paying the full hourly rate that I charge for the breakneck speed projects, they get charged for using the gear.
In other words I help the clients that record sensibly and come back.
Alan