this is very true.. they'll also be able to ask more specific questions such as just what you're going to use it for, what tyres you have and maybe spot existing wear problems, maybe even how you drive. .. show you a few different springs and explain the differences, etc, etc.
It can really depend a lot on the type of car, and then even amongst each individual car they might spot things that might make a noticeable difference (basic bushes being replaced, etc).