While having a screw loose can, up to a point, be likeable on a person, when it comes to your pumps, you’ll want all your screws to be sitting tight in their threads.
And there’s plenty of them on any average pump. From frame adapter mounting bolts and pump casing bolts to set screws and key on your coupling, all of these bolts and screws keep together key components of your pump and you would not want them to vibrate loose in any event.
By applying Loctite 243 to any of those bolts you actually eliminate several different potential problems. Securing them against vibration is just the most basic one. The adhesive will also seal out any air from the threads, preventing the bolts from rusting and seizing. It will ensure that the torque and clamp load are maintained, and at the same time make the disassembly much easier.
Gland studs and nuts are an even more sensitive story. If they happen to rust and seize onto each other, the torque required to remove them could cause the studs to back out. So I would rather recommend to use Loctite 2701 on the studs, which offers the same mentioned benefits plus the higher locking strength.