If you are a user that is comfortable building a family when you can't find one that will work for what you need it for, then you may be already doing this, if not, add this to your list of tasks when building a family and give yourself even more power.
If you download a model from a manufacturer, sometimes the families have sub-categories and sometimes they don't. If they don't, add one in the properties dialogue box.
If the subcategory you desire doesn't exist, you will need to create it. You can create any sub-categories you desire under the Manage|Settings|Object Styles property box. After creating them you they will show up in the drop down list below.
One situation where I have used this in the past is modeling of baseboard as a wall sweep (argue with me later about the importance of modeling baseboards). The sweep profile was given a 'wall base' subcategory under walls. Now in floor plans, the 'wall base' subcategory can be turned off to prevent a double line showing up at each of our walls where the baseboard occurs. Since the wall base is modeled, it will show up in any applicable 3D and elevation views.
Say you have a fancy piece of mechanical equipment in the project (for me this was a chilled beam). I can assign a subcategory of 'chilled beam' inside the mechanical equipment category and turn on or off the chilled beams in each view independently of other mechanical equipment.
If you have linked models and elements you don't want to see inside those linked models, find out what sub-category those elements have and create a new subcategory in your main project. By toggling the visibility of that subcateory, you can adjust the visibility of that element in your linked model (if the visibility settings of the view for the linked model is set to 'by host view'). This is a great feature, and very nice that the subcategories will talk between models. One important thing to note however, if replicating a subcategory from a linked model, the name must match exactly! Capitalization does matter!
