If you are using a wet and dry filter, not using substrate is fine because the wet and dry is essentially an external substrate that houses a huge population of BB. Wet and dry is an open system, so there is no danger of BB die off in power outage. But if you go with canister filters, they are closed systems and I will be concerned about power outage. In a closed system, BB can die off quickly in an extended power outage, and when the power resumes, there may not be enough BB left in the tank to detox the anoxic gases discharging from canister. Having a substrate in the tank will help, and it doesn't have to be thick, a 1/2 inch substate can provide home to ten to hundred fold more BB.
IME, a bare bottom tank shows poops more conspicuously than a tank with substrate which has the magic to quickly powderize the poops and hide them. So a bare bottom tank needs more frequent vaccuming than a substrate tank. If you have a lot of big messy fish, you have to vacuum a bare bottom tank everyday to look good, but with a thin substrate, you can get by once a week. Besides, it's not that harder to vacuum a thin substrate than a bare bottom tank, just use one of those wide mouth vaccum tube.
IME, a bare bottom tank shows poops more conspicuously than a tank with substrate which has the magic to quickly powderize the poops and hide them. So a bare bottom tank needs more frequent vaccuming than a substrate tank. If you have a lot of big messy fish, you have to vacuum a bare bottom tank everyday to look good, but with a thin substrate, you can get by once a week. Besides, it's not that harder to vacuum a thin substrate than a bare bottom tank, just use one of those wide mouth vaccum tube.
