I think it largely depends on which muscle groups you work. There’s different ‘‘dimensions’’ of training, some don’t need rest days. Complete rest or very moderate training? depends a lot on the attitude/way you do it, they are vague terms.
I could be just using my bicycle for everyday chores, and totaling maybe an hour of very light cycling, that I don’t even count into my ‘‘training’’ routine, or you may be resting on the couch not moving. Or maybe you’re lifting objects and not standing still for several hours cleaning up, working a physical job, etc.
From my personal experience, on myself, I feel a little bit of working around the sore muscles always gives me better results, and makes the soreness disappear faster. Largely also depends on how I am eating and absorbing food, and so many other factors… but allowing some circulation to occur, rather than complete rest, seems to work better for me. For pure max strain 1-rep strength (which i actually almost never do anymore, maybe more a 2 rep max at most), I’d certainly wait a couple of weeks. But that just means rest from that type of strain, not from completely not using that muscle group at all.
Similarly, I’ve found that when I get an injury, if I just rest and wait… it takes months (for example lower back injury during squats). The last time, which was probably the 4th/5th time I got this type of injury (lower disc moves, can’t even stand… had to walk up stairs on 4 legs), I immediately stretched it (in a specific way) the moment I got the injury. Allowed for slight movement and circulation around that area, never really ‘‘rested’’. After a few days I was already walking. The times before, the same exact injury, I would be stuck for months. This is not just me, also most other medical practices have shied away from suggesting complete rest (to pregnant ladies, to people that just had an operation, heart surgery, etc… before they used to assign ‘‘complete rest, don’t move’’, now they know that’s completely wrong… nothing worse than complete sedentary, in most cases).
In essence I think there’s a minimum amount of work that is better than being sedentary, in almost every situation. There’s certainly also a technique to it, not overdoing it.