you should never turn your filters off - the oxygen eating filteration bacteria will start dying off within minutes. always keep the filters going.

skimmers can be turned off periodically if you need some quiet, but then of course, they will not be doing their work in cleaning organics out of your water. you could compensate by having more live sponges.

it also depends on how heavily you have stocked your tank. most of us tend towards overstocking, so you can quickly overbalance with pollutants building up if you turn any equipment off (a real worry with power cuts).