I've tried tempo based reverbs where decay time is set by tempo. It wasn't as cool as I thought it would be. Dialing in by hand/ear works better for me. Predelay is a slightly more appropriate application for tempo based timing, but again, precision can be overrated, and I often find that dialing in what feels right is better than perfection for this application (usually want a bit under, because reverbs have some built in bloom time, or a bit late so the 'appearance" of the reverb stands out more). You can play with this by running a parallel reverb into a 100% wet tempo-based delay, by the way. In either case, I suppose one thing it would be good for is just ballparking a time for someone who isn't great at thinking in ms.