Calibre is a (tightly linked) set of
transactions that involve the Filesystem AND the database (db)
together. Get those delayed or interrupted, and you break the linkages. Allowing Multi-user (write) access is also a recipe for disaster. The data is cached during use for performance. Changes by the other user are not reflected when the final DB write is done.
Do folk get away with network stuff?
Yes...until it fails
(then they come here
for help recovering)
In the end: It is YOUR DATA (at risk)