This button could also be disabled (or set to 1 weapon only), so it does not affect those who do not wish to use it.
For melee, they may be able to switch between a range 1 weapon that does more damage, to a range 2 weapon quickly (I'm thinking, 250 sword vs. 175 sword is a good example)
For mage, they could swap between their staff, and no staff (which allows for short range healing); they could also switch between staffs of varying ranges perhaps.
For archer, I'm uncertain if any weapons are available at this time that would fit this criteria to be useful.
If this mechanic were implemented, it could allow for more variation in weapons to come, where you may decide to switch depending on the situation at hand. The prominent idea in my mind is, longer range with less damage vs. shorter range with more damage.
Just an idea... may never happen, but never know unless you post it
