lifters are just the plate that sits under the binding to give you more leverage for an easier turn, cause the higher up on a ski your foot sits, the easier it is to turn it on edge and carve a turn
get the lifters...u can always mount the bindings W/O the lifters underneath
if its a twin tip, then most people dont use lifters...i usually put the SMALLEST lifter i can find under a look binding, because if you mount them without any lifter, i myself feel like you lose some all mtn performance on the ski, but thats just my opinion on how i like a ski to feel and what lifters do for you
also, depending on how narrow the ski is, lifters prevent boot drag if you really lay the ski on edge and carve it