Are Grey Wardens truly needed outside blights?

Having Grey Wardens around as an independent organisation is probably beneficial to the world at large but I do question the necessity for all of them to take the Joining. The ritual itself is very wasteful of recruits who could otherwise still be useful doing general patrols and scouting. I also question whether the risk of contracting the taint is greater than the risk of dying from the Joining. So to my mind, between Blights when they are not needed at short notice to kill an arch-demon, it would be better to withhold the Joining unless the person actually did become infected, when it could then be used as an alternative to certain death.

People who live near historic entries into the Deep Roads, where darkspawn are more likely to surface on a random basis, are probably grateful for having an active order in the vicinity and appreciate the necessity for their presence there between Blights.

I would certainly agree with Nightscrawl that the independence of the Grey Wardens as a force not behold to any lord or state is a significant benefit to maintaining the order between Blights. However, it would seem that the current First Warden has somewhat negated that benefit by getting too embroiled in the political set up in the Anderfels. Of course this is probably what lies behind the conflict that was hinted at in Warden HQ at the end of DAI.