And this is simply a curiosity kind of question.

I know we do weight lifting and strength/resistance training mostly for body composition, but once you achieve your goals and get results that you're happy with... how do you maintain THAT? or I guess a better question would be, how do you maintain body fat percentage/body type as opposed to just maintaining weight?

To maintain you will have to continue working out, you can never quit, you can take a week or two break, but that's it or you will get right back to square one...

Even to maintain you need to make new goals every 4-6 weeks, that's the time it takes for your body to get used to workouts...

Well yes, but how do you make it so that your workouts don't cause you to continue to lose body fat? Like say a person's goal is to be at 20% body fat, how do they maintain that percentage?

Calorie maintenance. Basically, you will have exercise maintenance combined with calorie maintenance to keep you where you want to be.

I think that if you want to maintain where you are you would have to eat at maintenaince calories + lift at the level you have reached and not increase your weights or repetitions and not decrease resting time between sets.

That being said, I think our bodies are not going to be completely static through time without any changes, meaning there will be periods where you probably hold some more fat than others. It's typical when you lift weights to follow periods where you bulk to build muscles, you can make that in Winter months, and then periods of cutting fat in the Summer months. But even if you don't lift, in Winter we probably don't have the same opportunity to be outdoors and being more active so we would probably hold a bit more fat.

That's why I think even though you can be happy with your body there will always be room for improvement.

I think your body finds it's own % that you naturally settle at, aslong as you continue to eat and exercise for weight maintenance also studies have proven that lifting weights 3x a week will reduce bodyfat by 3% in 12 weeks without changing calorie intake, so activeity is essential