The choice to grow vegetables from seed is often recommended simply on the basis of being cost effective. While this is true, a more important reason may be to produce your planting material on site and within the environment they will eventually grow.
This germination of seed takes place mainly in the house before the slow process of hardening off (moving out towards the garden) begins. There should be no rush to get small seedlings outside. Even day time temperatures can drop suddenly and kill small seedlings. Keeping seedlings stable until the last frost or cold snap has passed is a tricky exercise in weather watching.