Doors and windows are the culprits responsible for most unnecessarily increasing heating/air conditioning bills. An unsealed opening as small as 1 mm could add hundreds to your heating or air conditioning costs over the course of a single year. Doors and windows MOVE. They have moving parts that wear out and loosen on their own. Wood shrinks as the moisture in the wood dries out. Many newer homes are built with wood straight from the lumberyard. The wood has a higher-than-normal moisture content and will shrink over the years.
Door and window hardware should be carefully inspected. In many cases a quick dab or spray of lubricant might do the trick. Squeaky doors and windows irritate some people as much the sound of fingernails scratching on a chalkboard. Lubricant is cheap. Don’t be cheap on the cheap lubricant.