A window might blow air out, but it also might blow air in. This would result in drawing your bathroom air deeper into the house instead of exiting it. A proper vent fan will undoubtedly move the air outside.
I don't think I have ever, in my life, been in a bathroom with a "proper" vent fan. AFAICT by observation, regulations must require a fan that makes seems to only make "chugchugchug" noises while seemingly doing nothing to the air.
Lots of vent fans in houses tend to not actually vent anywhere, or they're covered up with insulation. I know I had to dig my vent fans out when I moved into my house. Uncovering them led them to be much quieter and actually exhaust from the bathroom.
Good bathroom ventilation is important. Controlling humidity is a big thing, but also properly ventilating things like acetone or hairspray or other things along with bad odors is important.
> Lots of vent fans in houses tend to not actually vent anywhere, or they're covered up with insulation.
I do a lot of house repairs. I don't think I've ever seen a bathroom fan that goes outside except in mobile homes. They just vent into the attic. Same with many kitchen fans. They should all go to the outside otherwise they could cause moisture issues in the future.
I don't think I have ever, in my life, been in a bathroom with a "proper" vent fan. AFAICT by observation, regulations must require a fan that makes seems to only make "chugchugchug" noises while seemingly doing nothing to the air.