-You're body won't hate you: This is pretty much the top reason I do recovery days either in season or when I'm a midst a tough off-season regiment. Going through a recovery day will help get rid of the soreness that you feel all over.
-An off-day and still doing something: Recovery days give your muscles a chance to recover, because remember now kids your muscles don't actually grow and get bigger when you workout, they do it when you're recovering. You are in fact making little tiny micro tears, so it need s chance to recover. At the same time I'm not a giant fan of complete rest with exception of Sunday, if I can help it at least. Some days you just need it, but be honest with yourself.
-You don't want to be overtrained: This over laps a bit with the first 2 I just listed but I really wanted to hit on it. Simply put you're body can not handle being pushed 7 days a week 365 days a year or you will crash and burn and then get hurt. Even if you are Superman you are going to need some non resistance training days and some complete rest days.
Below is what I usually do for a recovery day or similar:
I usually spend plentiful time foam rolling, you should too, EVERYONE should. On days like this I spend about a minute per part per side. Even if it's not super sore give it that full minute and you may well find a tender spot you wouldn't have before.
|A1) Bench T-Spine Extension: 3x8|
|A2) Side Lying Open Book: 3x8/|
|A3) Quadraped T-Spine Extension/Rotation: 3x6/|
|B1) Dowel OHS against wall: 2x8|
|B2) Knee Break Ankle Mob: 2x8/|
|B3) Couch Stretch: 2x30s/|
As you can see really not too complicated, some upper and some lower, hope this helped someone out there today. Have a good day all and get after it today...even if it's just mobility.