When using a spotter, on the bench for example, a good spotter doesn't have to touch the bar to help with a tough set. Just the appearance of having the hands under or around the bar can help a lot of guy's complete the lift. If touching the bar is require, when the lifter slow's a bit or even stops raising the bar, than just the finger tips should apply a light pressure upwards. A lot of spotters will have their hands over, rather than under the bar, that can be a personal choice. If serious doubt arises that the lifter will not make a full rep and the bar travels back down even a inch or so, than that's the time for the spotter to grab the bar and help rack it. In a few rare cases a spotter may obtain a back injury due to the overextending of his body when attempting to grab an unexpected failure of a bench presser. Spotting for someone else will require full attention from the spotter (in other words, the catcher). Though tempting, it's not the time for checking out the booty call.
At my gym, when heavy benching, we will usually have one spotters on each side of the bar to catch the bar if needed. Also for squating. If people have a power rack for training than this will rid the need for on hands spotting when doing lockouts, dead stops, etc.. Those safety racks (stands), in my view, are not worth much at all. Good Luck.
