3D modeling I would define as being fundamentally intentional. Want a particular form? Make it as according to your intention!
Procedural modeling animation/simulation I would define as being 'overseen' by a mathematical algorithm.
In the case of the former, the artist has complete control over every aspect of the outcome.
In the case of the latter, the artist has limited control. Want to change the direction of that simulation-defined particle? Or that branch of that L-system generated tree? Good luck.
The advantage of a procedural approach is that it can realistically emulate the complexity of nature (which is beyond an intentional approach). Hence it's favor in those artists who are interested in nature.
