In a purely financial sense I would say they are a liability. Any extra resale value you might get out of the pool, you are probably going to be paying when you buy the house/put in a pool.
They do cost extra in utility bills and in maintenance costs.
I bought a home with a pool and am very happy with it. I grew up in a home with a pool, and understood the costs and work required, though. I also become part fish during the summer, metaphorically at least, spending alot of time in the pool.
I would estimate we spend ~$50 a month on pool chemicals, plus higher utility bills. The big thing is that its alot of work to maintain, if you do it yourself. Testing the water each week, adding chloring or PH balancers. Backwashing the filter(if its a sand filter), cleaning out the physical plastic filter once or twice a week. We have a baracuda that vaccuums the bottom, but it doesnt get everywhere so you have to brush the places it cant get to like the top step.
Of course, during the winter its cheaper to maintain because you dont lose as much water to evaporation, you can run your filter less often(basically just vaccuum the bottom once a week), and the cold weather stunts algae growth so you need less chlorine.
Just a personal choice. I love it, and put up with the extra costs and physical work. If you dont love swimming, then dont bother.
Are the maintenance and upkeep costs different if it's a salt water pool?