- Offline ensures that you do not suffer an externally caused downtime just before a deadline
- Offline ensures that you have a path for keeping your database throughout your research career, and to do system updates when _you_ want to.
- Offline ensures that if you leave academia, you will always have access to local copies of the academic papers you have referenced.
My favorite offline/local reference manager is `jabRef` [0] which stores all metadata directly in a bibtex-file. The GUI has an excellent pdf-integration, and everything is local and super fast.
Case in point: after a decade in industry, I am looking to get back into my academic fief. All the papers I ever read are in my Dropbox, and all I had to do to pick up where I left was download a current version jabRef and point it to my database which it read without any issues.