Soizic,
Not knowing any better, I was shooting everything into .EIP straight from the point of tether. IMO, using .EIP should only be used for transferring a handful of files to another Capture One user/station.
If anything becomes corrupt with CO, it's database, or a bad update, you won't be able to easily unpack large quantities of .EIP files very easily at all (this happened to me once after an update).
It's a great feature for throwing some files you worked on into Dropbox and then working on them elsewhere, but beyond that the risks really outweigh the rewards.