I'll tell you the same thing I tell our clients.

If you're not traveling to a place that's noted for fleas/ticks, and you're not currently or in the recent past had any problems with fleas/ticks on any of your pets, then no you do not 'need' to be on preventatives.

If any one of your pets has fleas/ticks, or you've had problems with fleas/ticks in the recent past (1-3 years), or are traveling to a place noted for having them (forrests, beaches, etc), then yes you probably should be on preventatives.

Hope that answeres your question.

I have 7 cats myself but every summer I put them on flea preventative (Revolution) because I do take them outside for walks, and a few of them travel with me to a place that has woods and is noted for fleas/ticks.