It is a dedicated mixing and hosting application that allows you to run your virtual instruments
If you cannot afford the full license, consider these legitimate paths: Vienna Ensemble Pro 7 Free Download
Professional composers use VEP 7 primarily for its ability to create massive orchestral templates that stay loaded even when switching DAW projects. It is a dedicated mixing and hosting application
Interesting fact: Some universities (like Berklee, Royal Academy) provide it for free to enrolled composition students via institutional licenses. Vienna Ensemble Pro 7 Free Download