You can probably state that having arms on your office chair is the norm for office furniture. It may even be the preferred choice by many workers, but there are a number of advantages that come with having no arms attached to your office chair that may convince you to give an armless office chair a try.
Convenience and Use of Space
Not all models of chairs will be compatible with your particular desk. Some chair arms arch up higher than others and can bump into a desk or the keyboard tray beneath your desk, making it difficult in some cases to maintain a good distance with your keyboard. If this problem disrupts the ergonomics of your desk, you may have to make adjustments to the chair, your desk, or somehow amend the situation. Sometimes you may also find that the arms of your chair get in the way while turning, reaching, and standing. Having an armless chair makes for a more versatile use of furniture. These chairs can fit with a wider array of desks without hampering use.
If armchairs are positioned or used improperly, they may encourage bad posture. If your keyboard is set on a desk, you may need armrests to perch your elbows on to reach the keyboard while keeping your shoulders relaxed. However, if you use a keyboard tray, using the armrests forces your arms and shoulders into an unnatural position that strains the muscles in those areas and causes them to stiffen after continued practice. Armrests may also encourage you to habitually lean on one side or the other. Maintaining this position distributes pressure poorly throughout your body and may cause muscle pain, back tightness, muscle soreness, loss of flexibility, and even headaches.
If you are unsure what you prefer, you may have an easy solution already at your disposal. The arms on most office chairs are removable. If you are hesitant about buying an armless office chair, try removing the arms of your current chair and see how you like it after a week or so (or enough time to get the feel of it and use it in your normal routine). There will probably be differences in how you move in the chair, what postures you use, and how you interact with your keyboard and mouse. Keep track of these differences and try to determine which type of chair is most comfortable and keeps you the most relaxed. Having or not having arms often comes down to personal preference, so decide what the most comfortable office chair for you is.