Alex,
Staples are often usefull for secureing a shrinkable carpet which has been overwetted (flood), except when the floor is concrete. However with a large carpet nails are a safer option.
In normal cleaning this situation should not arrise.
More normal uses of a staple hammer for the cleaner are:
1] Where a carpet has, in a doorway perhaps, has been addrift from its' smoothedge gripper for a while and the edge frayed beyond refitting, except by getting involved in a major carpet fitting job - The carpet is moved over the gripper with a knee kicker and the staples go through the carpet into the wood of the gripper. With care the staple can often be hidden between the pile.
2] When cleaning a Belgian Wilton I always thake the time to explain to the customer how the carpet is constructed and its' propensity for 'shrinking' if not properly secured. I then make an extra-carefull inspection of the fitment and staple where I feel appropriate.
However, in both the above instances, a staple gun is preferable because the staple can be placed more acurately, without bending the spike of a gripper and without the risk of takeing a chunk out of a skirting board.
John.