Mowing with a dull blade tears the ends of grass blades, leaving ragged ends which later turn brown, giving the lawn a dried-out look. Such grass blade damage also encourages the spread of fungus disease. Once a week is usually sufficient. Ideally, clippings should be removed after mowing. However, they can be left on the lawn if they are not heavy enough to pile up on top of the grass.
Heavy clippings can smother the grass.
Using a mulching mower is recommended if you want to leave clippings on the lawn.