The plants will grow much better from the nutrients in the compost but so will the weeds. The compost is black and with the weeds it will most likely, not pass muster with the wife.

I have never heard of compost being used in place of mulch, though compost can be used as a dressing. The compost will help to nourish the soil, though the compost wont keep back weeds, or help to keep the soil moist.

I use mushroom compost as mulch, and for the most part I much prefer it to regular mulches. Really I don't think of it as "mulch" but as top dressing. It improves the soil, in my experience even more than mulch. It will suppress some weeds, and although a weed seed will germinate if it lands on compost, it is much easier to pass a hoe over compost, so you don't have to hand weed or use herbicides the way you do with regular mulch. I think a compost mulch looks neat: it has that old fashioned clean-cultivated good soil look.

The one problem with some of the mushroom composts is that they form a crust in the sun. But a pass of the hoe loosens it right up, improves the penetration of rain/irrigation, and takes care of the weeds.

Bill