The short answer: Probably not.
You may know exactly what sort of practice you’ll have someday. Still, resist the urge to announce it in your AMCAS, AACOMAS, or TMDSAS essay. This is especially true if you favor a very narrow, competitive field.
Why? Because it takes some serious chutzpah to declare that you will be a urologist or dermatologist before you’ve taken a single class. Yes, you might achieve that dream, but your reader will not think highly of your boldness.
Remember your freshman year of college? How many of your peers said they were going to be doctors? How many changed their mind after Organic Chemistry? Same deal with medical school.
But there are exceptions to this rule. If you have great reasons for wanting to pursue a more general path—maybe you want to be a family physician or pediatrician—and you are applying to programs that really prioritize these tracks, then go for it!