Most homeowners cut too short, and they usually do it for the right-sounding reason: a shorter cut means more days before it needs mowing again. The cost shows up in August, when the short lawn is thin, stressed, and full of crabgrass while the neighbor's taller one is still green.
Grass height and root depth track each other closely. A cool-season lawn cut at three and a half inches holds a deeper root system, shades its own soil, keeps that soil cooler, and blocks the light weed seed needs to germinate. The same lawn cut at two inches is running on shallow roots in hot soil with plenty of light hitting bare ground.
A practical schedule for Rhode Island: start around three inches for the first cuts of spring, raise to three and a half or four through the heat of July and August, and drop back to about three for the last two or three cuts of the fall so nothing goes into the snow long and matted.
Never take more than a third of the blade in a single cut. If the lawn got away from you, mow it high, wait three or four days, then mow it again lower — cutting it back to target in one pass shocks the plant and is what causes that yellow, scalped look for the next two weeks.
Two more things that cost nothing. Sharpen the blade — a dull blade tears the leaf tip, and a torn tip browns off and loses water. And alternate your mowing direction each visit so the turf doesn't lean and the wheels don't rut the same lines all season.