Not strictly necessary, but a very good idea.
Theoretically, the driveshaft has been balanced and doesn't care about orientation. However, its balance can be changed once it's bolted to a yoke, and that's why we mark it.
I've found it useful, with all my XJ's, to take an engraver and mark the shaft for orientation and vehicle, since I sometimes work on a couple at a time. Just food for thought...
5-90