exhaust fans in bathrooms

[Anil J.]

I came across several posts suggesting to wire exhaust fan to the light switch in bathrooms so it turns on automatically when the light is turned on.

* This seems like it's based on assumption that people will turn on light. During Summer in California, there is plenty of light and a light is not required at all times, will people NOT turn it on?

* Does the frequent on/off of fan wear it out faster? (since we really only need it during a shower, and most people go into a bathroom for other reasons...)

What do you advise?