I like having a mounting hole no larger than 1/16" around the outer dimension of a pickup, cover or mounting system. I like keeping the instrument cut only deep enough to fit the pickup at it's lowest adjustment. If the cavity is too large or deep, the tone of the wood will be affected and more feedback is possible. Many companies cut large or deep pickup cavities to reduce the weight of the instrument or to fit many models and styles of pickups.
In the Custom Shop we once restored a 1956 Les Paul Custom of mine that was modified poorly for humbucking pickups. We rebuilt the cavities and mounted the pickups, making the pickups snug like I like them. Well, the guitar sounds fabulous with Antiquity pickups and it's one that I'm keeping for a long time.
WRITTEN ON JUNE 12, 2015, BY