heretic888
Explorer
It wouldn't. It would give you an extended rest after every N encounters (or, for more precision, every N XP worth of encounters). The question is, what value of N should be settled on?
There are two relevant considerations that I can think of: what effect does variation in N have on intraparty balance/dynamics? And what effect does variation in N have on the dynamics of the party vs the challenge?
Thinking about what happens if you have an extended rest after each encounter (which is the smallest possible value of N) helps work out what the effects will be on intraparty balance. And my contention is that, unless you're using martial E-classes, the effect is "not much". That is, again unless you're using martial E-classes, you don't need to worry about intraparty dynamics when choosing a value of N.
That then leaves the other relevant consideration, of the dynamics of party vs challenge. 13th Age is built around N = 4. 3E was (I gather) built around N = 4. I think, at least at paragon and epic 4e, if you use N=4 you will find that challenges aren't very challenging. Hence my suggestion that you might try N = 5 or N = 6.
Just to clarify, in 13th Age N = whenever the GM says so. The suggestion is for (roughly) 4 battles or so, but this is in no way a hard and fast rule. Personally, I hand out full heal-ups based on accomplishing "story objectives" or minor/major quests, regardless of how many battles that takes or how difficult they were (thus rewarding "clever" play).