Meh, a spring kit is one of those "ups" you only need, if you need it. IMO. So, you're having velocity issues and as part of the process of solving the problem you might consider purchasing a spring kit. Or you add an RVA and Palmer's Stab to your rig and want to play with input pressures so you purchase a spring kit to mess with fine tuning your input pressure while keeping velocity up.
Wow, I just sae this topic and the title "what is it good for" and then I started singing that song from the 70's "war ... what is it good for" and laughing to myself...
Forum 
