That is a good question, and one I don't know for certain but I know it is long-term. I would assume it is a year or more where the first year or two you may see no real benefit as the clover and grass compete, but at some point after a few years of clover recycling and putting organics back in the soil along with the grass, the overall nitrogen in a given area will increase.

We are talking white clover, which normally does not get any taller than grass. If you planted other legumes such as alfalfa and worked that back into the soil, the results would be much better.

Observation shows me that where I have clover in the yard, the grass grows MUCH better than without. I clover/grassed all of the trails in the front field which was almost completely tapped of nitrogen after being farmed for 100 years. The areas near the 6yo trail show better signs of health than away from the trail, even though tall clover naturally grew elsewhere. Makes for some really nice walking trails except when hot in the summer. Now have a pond down there to chill in.

The drawbacks are a non-uniform appearance to your lawn if trying to start in an established lawn. If you are starting a new lawn with both, it is easy to get clover plus grass to have a nice mix. The other drawback is an occasional honeybee may be stepped upon, leading to embarrassing hula-hula dances.

So a long-term strategy on a new lawn that is low maintenance once established is:

1. Till up soil plus Milorganite after taking a soil sample for current nutrient levels, remove rocks. This step is the most important as you will not loose much nitrogen after this point as with chemical fertilizers.
2. Seed with a mix of 100:1 - 500:1 grass to clover.
3. Mow once reasonably established.
4. Never apply weed killer, you will manually need to remove undesirables, but with a rich, healthy lawn this should not be very hard. Weed killer will kill clover also.

Of course grubs will live in the soil among many other pests, but the balance between what grubs eat, and what they don't will prevent any widespread damage from showing. If you have never treated the lawn with pesticides, natural enemies of grubs exist in the soil making it very hard for them to do any widespread damage.

Disclaimer: Skunks rolled by my lawn like a carpet twice in large areas looking for grubs. Both of these areas had no clover thus no roots to resist the skunks digging. A healthy organic lawn will draw in skunks/critters looking for a meal.