The concept of life support belts was actually initially considered for The Tholian Web,
before the environmental suits were settled upon.
According to http://en.memory-alpha.org/wiki/Life_support_belt
Although used exclusively in TAS, the life-support belt was invented during the run of Star Trek: The Original Series. Judy Burns, co-writer of "The Tholian Web", thought of using battery-powered "force field belts" in that episode, but the series' producers decided to feature EV suits instead. "They felt strongly that if they started something like a force field belt," explained Burns, "it might have ramifications down the line on other stories. I was a novice in those days, but today I probably would have countered that it was a prototype model that had been given to us this one time. In 25 years, we would get it back again." (Captains' Logs: The Unauthorized Complete Trek Voyages, 3rd ed., p. 72)
And yeah, as indicated by Metryq
, a few scenes throughout the series actually depend on the belts being there, through dialog and action. For example, there's that scene in Beyond the Farthest Star
when Kirk shorts out the helm controls with his belt, later also it appears that Kirk is using the belt force field for protection against the automatic bridge defense system [pictured at the top of http://en.memory-alpha.org/wiki/Beyo...Star_(episode)
], but my personal favorite, from the same episode, is [from http://www.chakoteya.net/StarTrek/TAS004.htm
and pictured at http://en.memory-alpha.org/wiki/Life_support_belt
(Scotty, wearing a life-support belt, is trapped by the cover of the core)
MCCOY: The force field of his belt won't hold that weight for long, Jim.
I'm really not interested in seeing them excised.