Mostly I run 6 days a week.
Trying to faithfully follow a 5K training plan (Garmin, with coach Greg) this week I took rest days, on Sunday, Wednesday and Friday.
Today as part of a Time Trial run I did 1.6km aiming for 5:12, which is my target 5K pace. To run at that pace I need to shift up a gear, but my legs just would not do it, and the 1.6 km came in at 5:23
Coach Greg still seems very confident I can sustain 5:12 for 5K a week tomorrow. Hmmm ...
I did the same Time Trial run last Saturday and averaged 5:08 no problem. (Didn't take those rest days!)
Lesson learned I think - it's not only OK for me to run most days, in my case it appears actually to be beneficial.
To be fair to Coach Greg on Thursday after I did his Stride Repeats run he gave me a pep talk (in video) in which he said it's fine to do lots more, and faster, running, than is in the plan, so long as your body feels comfortable doing it.
I felt bad after my poor performance in today's planned run so tacked on an extra 7 km, so at least my volume for the week is a bit more respectable!