What happens on star wars the old republic when you are using the free-to-play option and get to level 50

Basically, when you are using the Free to Play or the Preffered status options, once you reach level 50, there is not much to do. You are very limited on what you can do. The Free to Play option was created to give people access to the class story.
You are limited to 3 flashpoint boss loots a week, 5 warzones, and no operations missions. You can purchase a weekly pass (for Cartel Coins) for each of these to unlock them for a week.

Other than that, there is not much to do except explore, or do alot of crafting (which is limited to one crew skill).