It doesn't do much. i used to used it and have stopped.
The only preventative thing i use is Bti, because too often larva come with the substrate you buy and there's no way to avoid it without pre-emptive action.
the best preventative measures you can take, otherwise, is simply keeping a clean garden and control the environemnt. Don't leave fallen leaves to decay. Don't let RH go above 65 or below 30 etc. Don't get anywhere near the dewpoint -- primarly a concern after lights go out. As temperature drops, the absolute humidity stays the same but relative humidity rises as temps drop. It is surprisingly easy to get dew (condensation) on the leaves after the lights go out. A temp/rh probe helps here to avoid interrupting dark cycle of a photoperiod plant or if you grow autos, simply open it up and check on temp/rh/avoiding dew.
standing water on the leaves will grow "something" evenetually. Avoid condensation on leaves at all costs.
Bti will take care of any insects that come from larvea in the soil. Some stuff may still wander into your garden, but there's not much you can do about that. Have some pyrthrine concentrate on standby to mix up a kill-on-contact spray for bugs. Nothing is really safe to spray on a flower that you will later smoke or ingest (even if it's an extraction).
Just be clean and control the environment, and that'll take care of 99% of the potential issues. some people have dirtier homes than others, so a littlel self-reflection may be necessary, too. if you live in a sty, you may need to take more actions. Or, maybe you just have a ton of house plants that attract all sorts of potential issues. Your home may have elevated risks and require more effort.
Some sticky traps are good to have around too. I slap one up. In my garden it might catch 2-3 gnats over 100 days more times than not, but occasionally it pulls a bit more weight and they are cheap. the pack i bought 3 years ago is still half full.