When you mow, you prevent seeds from generating and so your lawn, in turn, will spread through its rhizomes frantically trying to find a way to regenerate. On the other side, mowing can be harmful in some respects as it can make the grass vulnerable to disease, especially when your blades are dull or unbalanced. It can also be harmful to roots if done too often, in repeated patterns and if it's cut too short.
example of rhizomes
Mowing too short is the number one cause for damaged and weed infested lawns. Just like with trees, the height of the top relates to the depth of its roots. Grass with deep roots have a better chance to survive a drought and it also keeps the soil shady, preventing moisture loss and drying of the sun, which in turn, compacts the soil.
The more blade surface the grass has, the more light it absorbs thus making for a good rate of metabolism. Pick a blade of grass and inspect it. As a rule of "green" thumb, cutting more than a third of the blade is too much. And yes, it depends on the type of grass you have as well as the time of year. Mowing too low to reduce the frequency of the job can be very harmful to the grass. It allows weeds to invade the lawn and causes the grass to be stressed making it more susceptible to diseases.
A sharp blade not only makes a great, clean cut; it also prevents a level of vulnerability for diseases. A clean cut across the top of the blade closes itself off, a lot like scabbing. When your blade is dull, it rips and shreds instead of cutting, making it more difficult to seal itself off from harmful diseases.
Mowing patterns should be rotated each time to prevent ruts in the soil, compaction of soil and the stress on grass roots. When you roll over the same spot week after week, season after season you are compacting the soil. This makes root growth difficult. It also makes water run off the top of the soil instead of sinking and absorbing into the root system.
We like to go north and south on one cut. Then east and west on the next. The following cut I'll go northeast to southwest, diagonally. Then northwest to southeast the next cut. Then the following cut from that I'll start the pattern again from north and south. After about a month of cuts you'll have established a beautiful plaid, textured look.
And never mow when it's wet or raining. The blades get coated with clippings preventing a sharp cut, and the clippings clump together to make decomposition slow. The clumps also block the light and produce dead spots if not cleaned up promptly. There are, however, times when extended periods of rain will occur. If this is the case, we recommend raising the mowing height as this will reduce clumping. And clean or scrape excess build-up of clippings under the mower AFTER obviously shutting off the engine and removing the spark plug connection.
For suggested blade heights for different types of grass see the mowing chart for your ideal lawn height.