different transplant question

[hoping4tomatoes]

Do you always need to transplant the seedlings? Why do companies advertise that you could plant a plug directly into the garden? I'm growing some in trays, some in styrofoam cups. Is it the switching of the type of growing medium from a germinating mix to a potting mix?

By the way, I used a Burpee growing greenhouse and it's not doing well at all. I used Gardeners Supply APS system for my test run and it "seemed" to work much better....Should have stuck with that for all of them...

So, do you really need to transplant?

Thank you...