I don't know if there are any studies on this. Personally it saves me a ton of time and mental energy. I don't have to remember the folder hierarchy when importing a function; I just reference it, ctrl+. (or whatever in your editor), and it autoimports. I don't have to remember or check whether it's SVG or Svg in this variable name. I don't have to remember what the fields of this parameter are, and so on. I don't get it wrong, build the thing, try it out, get a runtime error, and have to go back to square one to fix it. I think intellisence is useful specifically because it lets me stay in the realm of thinking about the problem/code, and avoid having to context switch to manage the details/minutia of coding.