Bathroom fans are essential for any bathroom to remove both moisture and bad odours to prevent the growth of mould and mildew. For bathrooms without windows, it is a Building Regulation requirement that an extractor fan is present. Even for a bathroom with a window, an extractor fan will do a much better job of removing the damp air than just opening the window will.
Two things to consider when choosing your fan are:
Fans are usually connected to the light circuit so that they come on when the light is turned on, and go off some time after the light is switched off. You can also buy fans with humidistats which automatically turn on when moisture is detected (and go off again once the air is sufficiently dry). A humidistat fan is especially useful if the lighting circuit is difficult to access – they can be wired entirely independently of the lighting circuit.
Of course a Fixington electrician can help you choose the right fan for your bathroom when you book in to have the work completed.