Depends on what your subject is, if your doing for... (
Interesting point about tinted windows and their combined effect with a CPL filter - I had never heard that before.
As for product shots indoors and using a CPL to cut glare, I guess that's a valid use but I have always used a light box of some kind for product shots (small stuff) - so glare isn't a problem and light boxes are very easy to make (probably a ton of step by step "how to" instructions can be found with Google).
It's important for people new to using CPL filters to remember that they are ineffective on metallic surfaces, so if you are trying to use a flash (for example) on something that is both metallic and causing glare, it's the lighting technique that has to be modified - and using a flash on a shiny metal object is always going to be a problem without properly getting the light to "cooperate" (up to the photographer to decide how to control the lighting). Using an on-camera flash is always going to be trouble - no less than trying to take a photo with a (on-camera) flash with a mirror behind the subject (a CPL will stop glare, but not direct reflections).
I remember working on a Hertz commercial back when all car bumpers were chrome - and lighting systems were prehistoric compared to today. We had a rough time with glare (seemed like everything was chromed then - windshield frames, window frames, even windshield washer blades) - we probably used so many large format Polaroid prints to test exposure that the cost of the Polaroids was very likely as much as a year's salary for me at the time.
In the end, the entire car was enclosed inside a tent made of sheets. The lighting was soft and outside the "tent" covering the car. The camera was inside the "tent" and a long exposure did the trick - (allowing a low level of very diffused lighting).
That shoot was done on a sound stage rented by the ad agency I worked for - like all large photo studios, there were no windows, so that's not a factor other than in home studios (even home basement studios usually have any windows blacked out).
I was showing my son the effect of a CPL very recently - so I did use one indoors. I took a photo of a framed picture of him with window glare on the glass of the picture - the image was completely invisible without the CPL but with it it was as if there was no glass in the frame at all, so I guess there must be uses for a CPL when shooting indoors if using natural lighting - just not something I ever did or gave thought to. But I can see where trying to do something indoors with light that you cannot control completely would make a CPL useful.
Funny how you can go decades and never come across some issue like this and other people might find it important the first day they pick up a camera - I guess it just goes to show that possibilities are unlimited.