If the fuel dries out it will leave a varnish residue behind. Tanks have to either be emptied or filled completely up. Just take a rag and stuff it down in the tank to sop up the little bit of leftover fuel.
I drain my 2 strokes before putting them away. You can also pull the spark plug and drop a few drops of 2 stroke oil in the cylinder and give it a couple of pulls. A couple of drop down the carb throat won't hurt either. It keeps rust from forming.