Some varieties just do better when they are directly sown into the soil, while others don't mind getting an early start indoors! Some varieties work well in both categories, depending on your zone/location.
Also Read: Tips for Successfully Starting Your Seeds
Crops that you would typically want to direct-sow are usually going to be grown in rows or clusters rather than as individual plants. Also, if the variety can take a very long time to mature, it makes for a good candidate for starting indoors.
Do your research to learn about what varieties don't like their roots disturbed! These should always be direct-sown to avoid any "shock" that would occur when you would need to transplant them into your garden.
Also Read: : "Common Seed Starting Mistakes and How to Avoid Them"