There is no easy answer here. The benefits of your office chair having armrests means that there is support for your upper limbs and reduced stress on your lower back while you are seated.  However, armrests can also lead to contact stress on your forearm and cause shoulder shrugging. If your chair is at the right height to your desk where your elbows are at desk height, then you don’t need armrests.  If your office chair has armrests, use these throughout the day when you are taking a break, answering or making a call, chatting to a coworker, or reading an email or document.