One of the primary reasons that most medications are available only by prescription is that there are risks associated with taking them (as with anything in life, even not taking medications at times). While you may feel fine, your physician is trained to look for signs of problems before they become symptoms to you.

Stimulant medications can increase blood pressure or pulse rates, or lead to a drop in weight for a few months or more. These effects and others need to be monitored, and documented by your physician, as part of the generally accepted "standard of care" for prescribing medications of any type. Some medications (not stimulants !) need periodic blood tests done to check for any effects on liver or kidney function. These side effects are rare, usually (not always) detectable early, and can become serious enough that checking every so often is worthwhile.

So if you feel fine, that's great. I want to be sure you will continue to do so, and that all is as well as you feel. That's my training and my part of our partnership - I do the doctor stuff. Part of your job is to let me know when you do not feel well, so we can sort out why together.