If you’d like to play standing up, or leaning against a tall bar stool, you’ll definitely want to use a guitar strap. The strap will allow you to hang the guitar off your shoulders and position the guitar properly, without trying to balance it precariously on one knee or overstress your arm and shoulder muscles.
If you like to play sitting down, you may or may not wish to use a strap, depending on how you prefer to hold the guitar. If you are comfortable holding the guitar so its full weight sits in your lap and does not create uncomfortable tension in your arms or shoulders, you may not need a strap.
If you feel it would be more comfortable to have the guitar’s weight partially supported up off your lap, you should try using a guitar strap. Using a strap will also allow you more room to experiment with adjusting the angle at which the guitar sits in your lap, which may effect your ability to make good clear chords, or to play certain right-hand techniques with greater ease.
Even a slight adjustment in the guitar’s angle against your body can have a noticeable effect in the ease of playing certain techniques. Using a strap allows you more options in finding the best angle for you.
You raise some great points to consider…
– Jeff Emmerson