Ground cover plants, what and why

[Ckbrew]

In viewing different grows I see some people use ground cover plants. Most common I've seen is clover and grass. I can see why they would be used for stabilizing the surface of the media in the pots. Are there other reasons to do this? What types of plants are good for this purpose? Is there any down side to this practice?

[Rwise]

Clover adds nitrogen to the soil, some plants repel bugs, some attract bugs (plant tobacco near your tomatoes), some add something to the soil. Plant carrots with your tomatoes, they help each other.

[Ckbrew]

Any particular type of clover for a coco/perlite media? I mainly am interested in stabilizing the top layer from getting divets when watering. Don't want to attract any bugs.

[Puglover1]

That's why I liked watering bags from the bottom up when I used coco/perlite, divots.

[Rwise]

Dutch clover does not get real tall, what I have in the field gets 3-6 feet tall.
I didn't cover harmful plants such as Black Walnut, kills what grows under it.

[Puglover1]

Hmm, I've buried three pugs under a black walnut tree, only weeds grew so I put rocks over the area. I did not know that they kill but I know they're not desirable trees here. Mine's straight and tall, on a ravine edge, wish I had the wood from inside it.