I would not advise adding plants to clean up the tank. You need a lot of plants if your tank is chock full of nitrates. If you add lots of plants and your fish like to have lots of place for swimming, then they'll gte really stressed out.
Don't use plants to replace water changes. It's just not a smart move, IMO.
I've read that plants use nitrates, give of O2 (though not enough to be significant, the water agitation is the greatest source of gas diffusion), make fish feel at home, give shade, make good places for adhesive eggs, good places for fish to scrape algae off of, and the list goes on.