Haha. Great question.. I guess it all depends on what is considered a “regular garden “. Many people will say the cover crop is part of a regular garden
A trend that is emerging in these environmentally aware times is biodiversity ..
planting in big blocks of the same crop can be a problem for the soil nutrients, pest control etc etc. and so cover crops/green manure are used. Nothing worse than bare soil .
But now. There are things like “forest farming / planting “ crops amongst the trees mixing it up. ( ok this is being explored in rain forest areas to preserve the environment. And also woodlands/farms around the world in small experiments)
But how does that relate to Regular garden. Well here in the uk we have a thing called the cottage garden. Originally a small patch of ground for the peasants to grow and provide everything they needed, probably with a pig and a couple of chickens in the corner ( actually the pigs would have a room in the house,the rotting manure and animals would help keep the cottage warm)
Anyway. The point is. Everything grown was mixed up. Fruit trees, woody shrubs and herbs flowers and vegetables when ever there was a space the next thing was planted.leeks dotted around a cabbage in that corner and another over there. etc. the point is there was never any need for a cover crop because it was always covered by crops. Any bare soil were just crops waiting to be harvested carrots, parsnips etc and they had the all the cut plant growth over them as a protective barrier which was then dug in no need for a cover crop
I could bang on ages yet. I did something like this in a large walled garden a few years back great fun
check out the permaculture association