Where problems usually occur (especially in my area) is when you have large temp/humidity swings from one day to the next. When those happen, the longer it takes for those changes to equalize inside the TT, the greater the chance for mold issues due to condensation.
Case in point - Monday we had low 80s and low humidity. Tuesday we had low 90s and double the humidity.
If I kept one closed all the time, I'd have some type of dehumidification inside the TT.
With top vents popped, temp stays consistent with outside temp. Much more difficult for condensation/mold to occur.
YMMV