Named Layer Filters (NLFs) have become a big issue with Autodesk 2005 products and Civil 3D is no different. For most Autodesk 2005 products their respective Service Pack 1's addressed a slow opening Layer Property Manager (LPM). They do so basically by ignoring all Pre-SP1 NLFs. They are still present, just not visible.
We often receive inquiries about the length of time it takes for the LPM to open. With the service packs installed older named Layer Filters, although still present, are ignored and not visible, in the LPM. This allows for the LPM to open quickly. The interesting fact is that these same named layer filters are still visible is pre-SP1 versions of the software.
After the installation of the SP1's, the moment a new Named Layer Filter is created all old layer filters were removed and only the new ones are left.
Either way this points out that many users have a tremendous amount of WASTED drive space because their drawings contain dozen, hundreds, even thousands of unused, unwanted, or unneeded Named Layer Filters. It is not unheard of that a typical drawing contains several dozen NLFs. These NLFs may constitute 100s of KBs of drawing size. If this is multiplied by the hundreds, or thousands of drawings on company hard drives, we have much wasted space!
This was all perpetuated by a practice that many consider a bad practice. That is to save a drawing to a new name and then erase all existing objects instead of using a drawing template (.dwt). This left the drawing with all of its existing NLFs. This coupled with the fact that all versions of Autodesk products up through 2004, when used to "Drag 'n Drop", "Copy/Paste", or "Wblock" an object from one drawing into another would copy all the NLFs from the 1st drawing into the 2nd. NLFs have propagated over the years to give us the current problems.
Users should be aware of the Named Layer Filters and take steps to manage them. There are many ways to remove unwanted NLFs.
By the way, the propagation of NLFs does not occur with the 2005 products.