I believe that depends on the spa. If you have removable panels on all 4 sides then you might want to have the room to be able to work on it.
If you opt for say the Artesian Piper Glen then I believe you need access to at least 3 sides to get to the 5 pumps.
From what I've read GOOD modern tubs don't have many leaks in the plumbing - they mainly leak at the pumps. I'm sinking my tub into a deck and will have a trap door access to the electronics and pumps. There will be limited access to the other 3 sides with one side about 2 feet from the house wall. Again I 'm banking on the fact that tubs don't leak in their plumbing too often.
Hope this helps!