The 5th-level spell teleportation circle says:
As you cast the spell, you draw a 10-foot-diameter circle on the ground inscribed with sigils that link your location to a permanent teleportation circle of your choice, whose sigil sequence you know and that is on the same plane of existence as you. A shimmering portal opens within the circle you drew and remains open until the end of your next turn.
You can create a permanent teleportation circle by casting this spell in the same location every day for one year. You need not use the circle to teleport when you cast the spell in this way.
The teleportation circle you draw seems to be a point of departure only when you cast it. When it's a permanent teleportation circle, however, it doesn't mention whether you can use it as a point of departure.
Can permanent teleportation circles only serve as destinations?
Permanent teleportation circles are for creating "custom" teleport destinations, such as a party's home base. Permanent teleportation circles themselves are only destinations, as you said. They don't allow you to teleport from them without casting the Teleportation Circle spell.