i only install them if a customer wants them. i don't have them in any of my personal basses, and IMO, i actually find them to be unnecessary, since i always make sure that the neck's holes are of the proper size and perfectly aligned with the body's mounting holes. if the neck's holes are stripped or mis-aligned, i just dowel them with maple dowels and re-drill them.
i have installed them several times in the past but i have not found them to be a cure or benefit for dead spots or change the tone in a positive way over a properly fitted/mounted neck using the stock 'sheet metal' type screws. so, unless you plan on frequently removing/remounting a neck on a particular bass (like going from fretted to fretless), IMO, there's no need for them.
