Weekly mowing keeps your lawn manageable. It reduces the amount of thatch (a tightly bound layer of dead grass, including leaves, stems, and roots, that builds up on the soil surface at the base of the living grass of a lawn1) which can suffocate your lawn. Weekly mowing produces smaller pieces of grass which will decompose more quickly and actually serve as a natural fertilizer.
Cutting a two-week growth of grass can produce unsightly clumps of clippings and require multiple passes over the area to break down the clumps. If the clumps are left to sit, the grass underneath will suffocate and the clumping piles are ugly. The extra passes over an overgrown lawn require a longer service visit and more fuel — costs which may be passed on to you.
Weeds thrive in longer grasses. Cutting your grass on a weekly basis will help control weeds before they can seed and multiply.
With a weekly mowing schedule, your lawn will always appear presentable and be ready for relaxing, entertaining, and enjoying your lawn without the headache of trying to do it all yourself.
1 Definition provided by Dictionary.com