Adjustable vs. Fixed Arms
Arms can adjust in a variety of ways these days. They go up and down, in and out and forward and back. For the most part, though, we can differentiate arms into two groups: adjustable, or fixed. Unless you are in a conference room, where the ability to rest your arms is important, adjust ability is preferred over fixed, in an ergonomic context.
Proper ergonomic thought deems your arms should not be resting when typing, as that slows the blood flow to an area that requires it because of the movement. However, the ability to adjust arms up and down, or downright remove them, can help prevent this.
Final Word: It is really dependent on the use of the chair. For conferencing, fixed is plenty. For cubicles, adjustable is nice. For big executive leather chairs, fixed is good enough. For task seating, adjustable is preferred.