I do low cadence 70-75rpm drills, often at Level 3/Tempo power levels. However, rather than it being a dedicated ride unto itself, I mix it in as an interval during a set. I do most of that kind of training on a stationary, though, rather than road. For example, just this morning I did the following set 3x, plus 10min warm-up and 5min cool-down:

5min L3 power at 70-75cad
5min L2 power at 95-100cad
5min L4 power at 85-90cad

Whether doing a whole road ride dedicated to grinding is beneficial would depend on your training program, or lack thereof. Being able to perform in various modes is part of being a well rounded cyclist; having the strength do low cadence hauls is another tool in the bag, and one that accepts attachments, too! You can pull out that low cadence to aid recovery at Tempo level, or you can marry the power to leg speed for L5/L6 action before hitting the HR limiter. So I think doing some work in that way is definitely good (i.e. low cad/hi pwr big ring stuff), it's just a question of how much/long/often, in my mind, and that depends on what the rest of the training regimen looks like.