Or here's another way to put it. I make mostly water models, but I am a forest ecologist by background, and so I do make the occassional "hero" or central character tree for the Vue community. 

 Even when there are fantastic plant generators available that allow people to either push sliders around to create a plant, or hand draw one, there probably still will be a need for someone like me to make hero plants.

When I model one for you, I am going to make one that is absolutely botanically correct, because I am a forest ecologist. I can't help myself, and why would I bother doing something lesser?  So, if you need to make a render featuring a Japaense Maple of some special kind, and the peole you expect to look at your render are capable of recognizing a Japanese Maple from a fake, you'll probably want my hero tree, rather than something you try to approximate yourself in The Plant Generator.

Or, I might make that same Japanese Maple in a very interesting and eye-catching shape. One that is particularly pleasing, and also poseable so that you can tailor it to your scene, and also use it over and over again. You might want to buy that from me because I made it be just so in a modelling program. Your chances of being able to "generate" something exactly like it in a plant generator are not so good.   

Some trees out in the real world just catch our imagination, yes?  They are distinct, unique and wonderful, yes? They stand out from all the others in the forest, yes?  But the other, more ordinary trees are still of very high quality, yes?  

Does this help explain the difference?