Yes; it is worth it if you have a lot of weeds where you are. But the insurance and liability are greater. Chemicals you know. Its more complicated than mowing. You need to understand the chemicals, weeds, insects, crabgrass and what will be effective. Plus you need suitable equipment. Experience as an applicator is very helpful.
If you pass the test in one try with an above average score--you can probably learn the rest. Read a few hundred posts here.
I agree with what everybody else has said. To answer your question. YES it is well worth it. Very rewarding in a lot of ways. I just got my license this year. In the past my lawns had more weeds than I could keep up with by mowing. Besides getting paid to take care of the weeds.. I just can't tell you how nice it is to pull up every week to see just about a weed free lawn. I find myself caring a lot more about the work I put in to my work rather than just mowing. The equipment I bought this year is all paid for too. Getting your license will not make you and expert. Continue to read and practice your trade safely. GOOD LUCK !!