I also use vacuum drying and built my own vacuum-oven (heated-temperature regulated and with vacuum down to 1 mbar now with new dual-stage rotary pump). By reducing the vacuum to sufficiently low levels at a given temperature you go below the boiling point of water. With sufficient low vacuum you can make water boil at room temperature.

As with Ama-fessional Molder above, I use a lot of varied filaments including polycarbonate and since very recently PEI. The later two both absolutely need vacuum drying before attempting a good quality print, every time. I also found that PETG is very sensitive to humidity but seems to have a kind of threshold. In certain weather conditions it can stay out in the ambient for long times without problem, with others it is a nightmare unless vacuum dried. ABS also has that tendency but to a lesser extent than PETG. PLA I use rarely as it can not withstand high temperatures or is too brittle for pressure-parts in my setups.

As a chemist I would like to add some more on humidity. The equilibrium exchange of water molecules from the air to the plastic and back again depends partly on the plastic and temperature, but mostly on the concentration of water-gas molecules in the air. It thus depends on the absolute humidity as opposed to the relative humidity everyone keeps on mentioning. The definition of relative humidity is the actual absolute humidity divided by the maximum absolute humidity capacity the air can have at a particular temperature (hence relative). However the latter is strongly temperature dependent. A relative humidity of 50% at 18 Celsius means 7.7 grams of water per m3. A relative humidity of 50% at 32 Celsius means 16.9 grams of water per m3. Although the relative humidity is the same, the latter absolute humidity (on which the equilibrium with the plastic depends) is more than twice as high. You can google around for absolute humidity calculators and play around with them to get an idea. For example try to find out why there is also an industrial process called freeze-drying.