Question about RR schedule

I'm loving the RR, and I'm making more improvement with this routine than any other that I've tried.

However, I'm very new to the concept of rest days in a workout schedule. The RR suggests that you work out 3 days per week, but that leaves an extra rest day on the weekend.

Would simply doing the workout every other day be too much?

Basically, it's working out 7 days out of two weeks (mon, wed, fri, sun, tues, thur, sat, mon, etc).

Does the extra rest day per week serve a specific purpose? Or is it just a quirk of having an odd number of days in the week?