A quick question here: is there any disadvantage of leaving MKR in the voting contract until the next vote, in order to save some gas fees?
There is an advantage to leaving your MKR in the voting contract. MakerDAO uses continuous voting, so if you have voted the most recently executed spell (which usually has the most votes and is called the “hat”) then you are protecting MakerDAO by leaving your vote there. This protects the system from a potentially malicious spell because a new executive spell must have more votes than the current hat to be executed.
There is no disadvantage to leaving your MKR in the voting contract (except potentially if you had some other use for it other than securing and participating in MakerDAO).
You can find more information on voting here.