The use of mulch in your garden can be very beneficial for a variety of reasons.
A good layer of mulch prevents the seeds of many common weeds from germinating; resulting in less time spent pulling weeds in your garden.
Mulch helps retain soil moisture resulting in the need to water your plants less frequently.
Mulches help improve the soil by adding organic matter as they decompose. These added nutrients are very healthy for the surrounding plants, resulting in less of a need to compensate with additional fertilizer. Grass clippings (although less attractive) can also be used as mulch and decompose much quicker than bark mulch.
Adding mulch to your garden is inexpensive. To be effective, a layer of about 2-4 inches is necessary to provide the benefits listed above. Mulch should be applied to a weed-free soil surface. Simply adding mulch to a flowerbed full of weeds will not prevent the weeds from growing.