If you want putting green quality grass forget this idea. It does not produce a manicured look. It looks just like grass cut with a regular mower after a couple of days growth. How far the roots go down depends on how high the grass grows up so 7" grass is much more drought tolerant. I don't water at all. Stop paying sewer charges for water that doesn't go down the sewer.

Anything you do to help grass grow like aerating, watering and fertilizing also helps weeds to grow.

 Longer grass collects more dew overnight. It spreads faster as well. I used to have many bare patches. The wheels are mounted behind the weed whackers so they don't trample the grass in front of cutting it. Much easier to push around than a push mower since it's only 20 lbs. A single 15 amp outlet can easily power three 4 amp 12" corded weed whackers. There is 1" of overlap. The middle one is held with wingnuts so it is easily removed if you want a single weed whacker. 

Weed killer is illegal on lawns in Ontario so most people have to put up with dandelions and other weeds. Taller grass is a much more environmentally friendly way to eliminate weeds without any effort or cost.

In 100% shaded areas where it was mostly bare with yellow grass I encouraged moss to grow. Moss has no roots so to encourage it you need to keep the surface moist with a couple of minutes of water mist every hour. Most water timers can't do this many very short cycles so I built one with a controller. That is one of many $$$ saving projects at https://sites.google.com/site/nodemcu12e/. Now the area is bright green year round and no watering is needed. Zero mowing or any other maintenance.

 The only time I use the gas mower is late fall so the grass is short over winter and not matted in the spring. I could modify the design so the cutting height is easily adjustable over a large range and not use the gas mower at all.

I have been using this mower for the last 5 years and the grass has never been better.