Curious to how often you remove large objects, such as driftwood, large rocks and so forth to clean under them, ie gravel clean. It's a huge pain especially when most are being used by the inmates to breed.
I use my gravel vac about every other week and just do my best to get all the accessible areas. I remove everything about every 2-3 months and do a very thorough cleaning.
One way to tell if you might need doing this is to monitor your water quality over time. If you have not changed your stocking level but your nitrates are higher than you would like when you do your water changes, then you should probably do a complete vacuuming.
For instance, my average tank has about 10ppm nitrate when I do my water changes. If it was higher than that twice in a row, I would probably remove decorations and do a more thorough cleaning.