Microclover won't outcompete the lawn, it's just not that competitive and, just like any other stand of any plant, it'll also get weeds that you have to take care of. However, being clover, it's also susceptible to some of the herbicides you'd use to knock out other weeds, including other clovers, oxalis, and so forth.

Adding it to the existing lawn will get you out of feeding your existing lawn for the most part (you still should, just not nearly as much or as often). The stuff is really more of a helper plant than a groundcover on its own. It's usually used at about five percent of the lawn grass seed count.

Microclover, just like grass, would require watering during periods of extreme heat and dryness, although it'll need less water than most grasses. So you aren't completely out of the woods in terms of "lawn" care. :-)

You'll also have a lot of bees, which may or may not be a concern for you. Personally, having dogs, I'd rather not have said bees at grass level but clouds of them in the gardens are fine with me.

And lastly, clover is moderately wear tolerant, so it should be competitive with the lawn--but I've never tried it as a monoculture.

Depending on your locale, there may be other lawn alternatives that would serve you better?

Yes, where do you live?

Apologies for delay in reply ... I live in the San Francisco bay area, east towards Sacramento where it's a bit warmer/dryer.

If you have full sun, try UC Verde buffalo grass. It goes in as plugs and will spread far and wide fairly quickly to become full and dense. The mowing, watering, and fertilizer requirements are much lower than for almost all other grass types. This grass will thin out in the shade on the north side of a fence, building, or low shrub. If a tree has a high canopy, it should be fine.

If you don't like that, then a "dwarf" (actually just slower growing) type of St Augustine would work for you. St Aug is much less hassle than bermuda if you want the bermuda to look nice.

I seem to recall a discussion about microclover on a forum somewhere. What the owner found was the micro leaves became regular clover after a season or two.