When organizing imports (Command + Shift + O) and having enabled "collapse into single import statement" it will produce code in the following format:
import net.liftweb.http.{Req, PostRequest}

While if you use format (Command + Shift + F) it will reformat (given you make some changes in the mean time) the existing code to the following format:
import net.liftweb.http.{ Req, PostRequest }

I prefer the spaces in front and behind.