Yes, but not often in convenient places. Many of the powered monitors (like my M-Audio BX8s) seem to have been designed on the assumption that they would be used with other gear that had gain controls, so they put the knobs where they are not easily reached. I run them off a digital mixer so I can turn them up & down from there. It's a good idea IMHO to have some sort of device to do that since it's important to match the outputs of the monitors for good imaging and you sure can't do it by lining up the marks on the knobs! I set mine with pink noise and an SPL meter and the marks on the knobs are somewhere around 20 degrees off from each other. Whether this is due to variation in the pots or (what I think) differences in the acoustic environments of the 2 speakers I'm not sure, but it wouldn't do much good to be constantly turning them up & down by ear.
