For grasses in most regions, bagging in the spring and fall is optimal. This reduces thatch and leaves an overall neater appearance. This requires a bit more work as bagging, clippings and disposal takes additional time. However, it will yield a better result. During the summer months when turf is not growing as vigorously, mulching and or discharging the grass will be sufficient. But you may have to make additional passes to evenly distribute clippings for a neat appearance. Over-mulching of clippings while turf is growing strong in the spring and fall will be counter-productive. This will cause thatch build up and can choke out the healthy turf. It can also impede new seed germination in the fall.