Top answer!

I would add that depending on the type of assignment, you might not have the time to write your own exploits. Nowadays, everything is sold as a pentest even though a lot of the assignments are vulnerability assessments, where you don't have the time to fully exploit the vulnerabilities you find. In these cases, the difficulty lies in managing time and often, showing that manual exploitation is possible is as far as you can get before you need to head on to the next bug.

But more importantly.... good luck on your OSCP exam!