Other jobs require more focus
...but you might learn more about agility
When I first started I was scared to do jobs like scoring or timing. I was lucky enough to have someone encourage me (ok she basically said go sit in that chair and I'll tell you what to do) to try scribing. What I found was by scribing, I actually learned so much about agility. I learned more in that one afternoon than I had taking multiple classes. I'll never forget and am forever thankful. Scribing and timing can be intense. There is much responsibility as you are the key to keeping the trial moving as well as documenting scores. But these jobs are two of the jobs you will learn the most.
Some jobs you do on your own time
There are jobs at every trial that don't require you to loose focus during the day. These jobs include set-up and tear down of rings, grounds management (garbage), hospitality, workers raffle, ribbons, etc. All can be done when it is convenient for you and perfect for the competitor that needs to focus or has multiple dogs running.
The big jobs
The final group of jobs are the jobs that get the trial up and running. Trial chair or secretary. These are jobs that require work before and after the trial. During the trial there are trouble shooting duties, dealing with complaints or problems, or just making little decisions...but most of the work is done before the trial starts.
None of the jobs I've listed are paid. Clubs differ in compensation, but must clubs will give free entries to individuals who do jobs like trial chair, score table, course builders, etc. The jobs that require you to be available when it might not be convenient for you.
Some clubs (SMART and Bayteam) actually will pay full time workers (if you are not running a dog and work the entire day. Full time working is a great way to pay for future entries.