To add to what Zsigmond Rab said, it is important to note that LAR imports is not a good "bulk import" mechanism.
Basically the LAR import involves repeatedly calling the Liferay APIs to add individual information, and for large LAR files this is usually a bulk upload. The LAR process is not tuned for bulk loading. For example, when importing users there's the add to the database followed by the update of the index, possible ldap synchronization, ...
Now, if I had to bulk upload a lot of users I certainly wouldn't want to do it as a LAR import. I would build a tool to do the database inserts w/o index updates, ldap, etc. Let all that crap wait until the db population is done, then trigger index rebuilds, ldap exports, ...
You get the idea.
Note, however, that I am not advocating updating the DB directly - this is still a no-no. You have to see how the Liferay API handles the load of the individual records to ensure that all of the same things happen, and this is not something that you'll see by just pushing into the table(s).
