There are a three options for connecting the pouch and baseplate in a two piece pouching system.
One disadvantage to the mechanical snap is the hand dexterity it requires. You have to be able to squeeze the two pieces together all around the pouch coupling to make sure it’s securely snapped in; people with arthritis in their hands, or other hand dexterity troubles may struggle with this kind of system.
The disadvantage to the adhesive coupling it making sure you stick the pouch on to the baseplate in the right place and get it secure. It is easy to think you’ve stuck it on snugly and later find out there was an air pocket, which inevitably leads to a leak between the pouch and baseplate. One way to get around this would be to stick them together before you apply them to your body, but then you might as well wear a one piece.
Some manufacturers of adhesive couplings advertise that you can remove the adhesive pouch and stick it back on without compromising the adhesive, though that is not always the case. When removing the pouch sometimes output gets onto the part where you need to stick the adhesive, forcing you to clean it off before trying to stick the old pouch (or a new one) back on.