It is one of the pertinent questions which you should ask a contractor. This question would help you to assess the popularity of the contractor. If the contractor is only working on your project, then note there might be something wrong. Ideally, the contractors collaborate on a variety of projects at a time. However, also remember that if a contractor works on too many projects at a single time, it may affect your project too. This is the reason to clarify with them about the number of projects they are working on.