Yes. I have done this for many years. Some vegetables require a long maturing time which can only be accommodated by sowing early.
Also to get early crops of peas and such early sowing and planting out after the chance of frost has eased is a good idea. This also adds to the value of sowing early as many early crops can be expensive in stores.
Sowing flowers early also gives you a longer period to enjoy their blooms later in the year.