Should I use return keyword when rendering a view?

In your case it doesn't matter at all. However using return is a common method when using conditionals. For example:

app.get("/", function(req, res){
  if(req.whatever) {
    // Using return here will cause any code after to not be run
    return res.render("index.jade");
  }

  // Default action
  res.render("default.jade");
});