I have a boost/vac gauge and Cluster Bezel. The only thing I do not like about it is the gauge won't go all the way back into it.
Other than a boost/vac gauge I also have a useless nb02 gauge. I just bought that to fill in the extra hole.
I just wanted the boost/vac gauge to make sure everything was working right. For example I wanted to make sure I was at 7-8psi not, 14-15.
It also helped me decide to take off my boost controller when I saw the boost keep climbing past 11.
I know s/c don't have boost controllers, but it could help if you have belt slip, or something along those lines. But if you have a MAP sensor and tweecer r/t you could just watch it there.