Trickle, boost switches, what are they for?

[Travelcrazy]

We are buying a house and spotted a few of these but forgot to ask what they do?
Can someone please explain them to me.
Thanks

I tried Google but none the wiser 😅

I assume bathroom extractor fans?

I have just googled, also used for manual heat recovery, same system ie an extractor fan removes stale air but then can input fresh air which is heated rather than just cold air coming in.

Thanks for the reply but I still don't understand it