tonton2, It's really a personal choice, I don't think any answer fits everyone. I organize all my source footage and pics (~15TB) on a particular drive letter in a hierarchal fashion, and then just bring those into PD as needed. My source essentially stays untouched and is always available and in the same place (drive letter wise for easy PD compatibility). If I have old content on a non active drive I just mount the external backup drive in a dock and give it my universal drive letter and then all the pds projects I've created and saved on the drive reload just fine, except for PD anomalies.
The bad part about "Pack Project Materials" is it duplicates all "source" clips in the pack as it's named. So, if you use little bits and pieces of several large source files in multiple projects, you get everything duplicated every time. It's good for sharing an immediate project, in my view a wastey long term retention method. I've also found through the years that it does not necessarily pack everything that was used in a project either so not as good as it sounds.
My video is redundant on another backup drive, one can simply use any sync backup utility or I often simply use Windows robocopy command as it's easy to sync a redundant drive for backup purpose.
Jeff