Office Web Apps Server : Lync 2010 vs Lync 2013
Users with Lync 2013 can experience the full capabilities of Office Web App Server; only users of Lync 2013 will be able to do such things as scroll through PowerPoint slides independent of the actual PowerPoint presentation. Users who are not using Lync 2013 will still be able to join online conferences and view the PowerPoint presentation; however, they will not be able to independently scroll through the slides, nor will they be able to see slide transitions or view embedded videos. Note that these capabilities will always be available to users of Lync 2013; this is true even if the PowerPoint presenter is running Microsoft Lync 2010. If a PowerPoint presentation is being hosted by a user running Lync 2010, Lync Server 2013 will coordinate with Office Web Apps Server to make sure that Lync 2013 users will view the Office Web Apps Server version of that presentation. Office Web Apps Server does not provide PowerPoint services for users running clients other than Lync 2013. Instead, those users connect to the Conferencing server service and view PowerPoint presentations the same way they did in Microsoft Lync Server 2010. This also means that these users will only have access to the more-limited capabilities offered by Lync Server 2010.
Office Web App and Internet Explorer
Although no client configuration is required for Office Web Apps Server, it is recommended that conference attendees be upgrade to Internet Explorer 9. Although conferences can be accessed using Internet Explorer 8, there are some limitations to using that Web browser. For example, users of Internet Explorer 8 will not be able to resize the PowerPoint stage to a custom size; instead, they will be limited to using one of three predefined stage sizes. Likewise, Internet Explorer 8 users will not be able to play media files.
Note : If the meeting was scheduled on Lync Server 2013 and PowerPoint slides were uploaded by a Lync 2013 client, Lync 2010 users have view-only access to the slides.
Note : Overall, I always suggest the customer to upgrade user’s client to Lync 2013 and IE version to IE 9 or later as soon as possible. At least it reduces the chances of support tickets to be raised for many obvious limitations. :)