Obviously it depends on the type of work being done. That being said there are certain universal management duties that require a little understanding:

1. Time management
Managers who do not understand the work will often set unrealistic deadlines and have unreasonable expectations.

2. Promotions
It helps to be able to see who is actually doing a good job vs. the brown noser who appears to be doing better and is actually riding the coattails of the people who deserve raises.

3. Advice
When there are problems the management is looked to for direction. It's hard to settle disputes or give any sort of advice if you don't have a clue what it is you are managing.

In conclusion, management skill is of course #1. Now that you have the job, do your homework. Take some time to really get a good idea of what your subordinates do on a daily basis. It's okay if the material is over your head but crack a book. If you can't understand the subject matter at all it should give you a better respect for your team.