There’s a misconception that you should detune your guitar before storing it, as this lessens the string tension over the body and could potentially extend your guitar’s lifespan. In reality, there’s no reason to do this with a steel-string acoustic or electric guitar. These instruments are built with something called a truss rod, which is a metal rod that goes down the length of the guitar neck. Its purpose is to counteract the tension of the strings, taking the pressure off the body itself. That said, if you have a nylon string or classical guitar, it may not have a truss rod, so detuning your strings before storing may actually have tangible benefits.