Doesn't this also depending on mileage and intensity as well. At my old age, I completely got rid of the recovery runs or easy days. I will just take a day off instead. All my runs are 11 to 13 miles now and mostly 6 days/wk. Trying to cleanse the body and put in deep base miles after such a long layoff. I am coming back to serious running after 20 plus years of lay off.
At least in hindsight from my younger days, I think taking days off is not that bad. I rather "digest" the runs than go out there all tired and sore. But I guess it differs from person to person. I imagine if you're running close to at least national class level, maybe 7 days or more is necessary. Everyone trains so much harder now than when I was younger.