Why does lync read/use OAB outlook files?

How have you recognize that lync use the OAB? Normaly the lync client will download his own global addressbook from the lync webservices.

You can't delete *.oab files from the profile when you close Outlook and Lync still opened.
If you close Lync you can delete OAB files from Outlook.

Bump.. Will someone please answer the above question? Here's an example of how I see OAB Outlook files being used by Lync:

In Lync I can search and find Distlists (To mass add Contacts) when I have OAB files in place. Once I delete the OAB files, Lync no longer shows Distlists in the search results, however, it still seems to find possibly users who have a SIP address. In fact I have many Lync clients that do not find distlists, wondering if this may have to do with the Outlook client not being in cache mode, thus, no OAB file in place.

Since this is Lync 2010 Forum
the answer from Holger is correct

Lync 2013 Contact Card on the other hand does consume and sometimes overrides information from Lync 2013 Client if OAB is in place,

if you enable cached mode in Outlook then this behavior will not happen