When designing Revit families, you have to always keep in mind the level of detail you are putting in to your families, and the affect this will have on the performance of your project. When you have a large project with numerous families you may notice that your Revit starts to run slower, even when you are doing tasks unrelated to the detail of the project e.g. printing. One of the reasons for Revit "under-performing" could be the visibility settings setup or level of detail of families in a project.