I don't have an indoor cat, but my friend has one, and I was wondering if it needs flea treatments. He doesn't give it any, and it seems to be okay, but would giving it a flea treatment(s) be good for it, and if so, how often?
We've never done that with our cats as they're indoors, but the risk of fleas being introduced into the house through other means is probably your basis for consideration. If there is some chance of wildlife making it in or other pets visiting (like a friend's dog), then you might consider it. However, if it's gone this long without the treatment, I would probably deal with a flea situation as a one-off using flea soap when, or if, it happens.
Why put the poor cat through the indignity of a bath if you don't need to? Doing that is not a lot of fun...
Mind you, you could consider the spot-on treatments like Advantage Multi as a way of preventing. It's not hard to do and effective. As I said though, if there is no evidence of fleas, why do it?
If fleas have a way into your house (via a dog, for example, or if you spend a lot of time outdoors in woods), then your cats could still get fleas that way. If this is the case, I suggest you use a flea comb regularly to look for flea dirt. A flea comb has extremely fine teeth; comb the cat every day and use a white cloth or tissue to wipe off the combings. Then look for small black specs. (These are dried blood, not flea poop, from what I understand.) Flea treatments don't innoculate the cat against fleas, so if there's been no exposure you don't get any benefit from the treatment from what I understand (but see below). Or so my vet has advised in the past; I'm not an expert on this. So, in general, you can wait for evidence that you have a flea problem before deciding to treat for it. (If you do treat, follow the package instructions, which vary.)
However, there may be non-flea-related reasons to use a flea treatment sometimes. Some topical flea treatments treat fleas and other conditions (like heartworm). If you want to treat for one of these other conditions, it's worth asking your vet about whether to use a flea treatment to cover both. One of my (indoor-only) cats is getting a flea treatment not because of fleas but because of other allergies, and it seems to be helping.
Speaking from experience here: my husband and I purchased a house 18 months ago. Our 3 cats never go outside, but earlier this year we needed to flea treat the cats and the house.
The previous owners had dogs who were inside and out, and the very mild winter plus us not realizing there could be an issue meant that over the course of a year the flea population built up to where they became a problem.
It doesn't take much for fleas to take hold - we had no sign of trouble our first summer in the house, but by the next summer it was ugly.
I'd say that if your friend's cat stops whatever it's doing to bite and groom at the base of its tail or scratches a lot around its neck and behind the ears it's worth checking for flea dirt (tiny black specs) and egg cases (longer black bits that crumble under pressure). If your friend finds any, then he's going to need to treat the cat and also treat his floors and other surfaces to kill any fleas or eggs in the house. Usually it's a dose every 6 - 8 weeks unless you've got a severe infestation, when you treat more often. Also, older cats are more vulnerable to fleas so they need to be watched more carefully.
If there's no sign the cat has flea problems, then there's no need to treat it.
I have had 3-4 indoor cats. Two of them I've had for around 14 years. One of those, is/was a jailbreak artist who has managed to leave the house for her own adventures typically lasting 6-12 hours.
I have NEVER ever had flea problems. The only time I used flea / parasite treatment was when we adopted the second cat (who we literally found on the street).
I have heard of indoor only cats that never go out getting fleas (the exact mechanism is unknown, perhaps fleas go through some opening in the wall, perhaps squirrels, raccoons, mice, whatever bring the fleas in).
But I wouldn't treat for fleas unless you have fleas.