As a young believer, my Presbyterian pastor asked if a man is called of God to an office, how is he uncalled if he has never demonstrated that he is unfit? If a deacon or elder is called this year, is he suddenly uncalled exactly two years later? In recent years, I've seen officers given sabbaticals so they could come back and serve refreshed, and I've seen folk reach ages when they can no longer reasonably serve and step aside, honorably.
My church does 3 year terms for elder and deacon. As someone who has done one "full term" as deacon and was ordained as an elder this year, I have been reflecting on this more, as I'm not sure our system is ideal. We do have a process (based on our FoG) to honorably retire those who are unable to serve any longer as "Elder Emeritus." We do still recognize those who are not currently in office as ordained to the role. Our inactive elders are generally quite active in the service of the church even though they do not currently serve on Session.
The biggest disadvantage I am feeling is that is hard to have as much continuity. 3 years is a short term, so folks are rotated on and off frequently. For us, it's mostly rotating within a group that has been serving on and off for years, but seeing as the time of "break" may vary, it makes it hard to have a conversation and build on topics overtime. Another disadvantage I feel is that we have a nominating committee every year which is a lot of work.