If you run a compressor powered roof pump you should definitely "drain daily" as instructed to do so by the manufacturer. Especially in humid weather and also when using wheelbarrow compressors with small tanks. ALOT of water builds up in the tanks in a short period of time in humid weather. The more water in the tank the less volume of air there is and therefore the compressor will work harder and trying to keep up due to less reserve air supply.
Draining daily can be a pain though with the little pet****(s) that can be hard to get to.
Here is what I do:
On my wheelbarrow compressor I remove the pet****s and "T" the two tanks together and run a hose to an easy accessible spot on the compressor, in my case towards the front near the tire,..there's a little "bumper" bar there. On this hose i put on a metal ball valve and attach it to the little "bumper" bar.
Now, when you need to drain daily you can just open the valve and empty the tank of water. There is no need for the "drain" to be on the bottom of the tank. The compressed air will push it through the hose just fine.