Visual Assist and the built in Intellisense tooling share a few common features. Where we share features, VA frequently operate much faster and do a better job of giving you the correct results (e.g. finding more references that Visual Studio would miss).
Also, the Visual Studio UI can arguably complicate some dialog boxes for simple tasks.
An example is the Visual Studio unified search, which operates like the search bar in the operating system wherein everything is shown. In contrast, VA uses different search dialogs for each type of search, each with features specific to that kind of search and without displaying results you aren’t interested in.