Seed suppliers offer pelleted seed for a number of plants and in my opinion, the extra cost is justified. Many seeds are so tiny, like petunias, and it is difficult to see them which makes it a bit of a challenge to sow one seed per cell. The clay coating makes it easy to sow and eliminates the requirement for thinning. Another benefit is that some plants are better sowed in a clump of 3 plants. Bacopa pellets have 3 seeds per pellet. There are a few "combo planting" options too. "Fusables" come to mind which essentially is one pellet with a combination of plants or varieties. For example "Fusable Silk and Satin" is one pellet with a Pink Easy Wave petunia and a Snowtopia bacopa. Basically it allows you to sow a combo from the get go. All pelleted seeds are surface sowed.