As already mentioned in #Lync Question 1, Lync Server 2010 introduced the requirement for cookie presence/affinity with the mobility service.
For Lync Server 2013 the requirement for cookie affinity has been reduced however this depends on using the Lync Mobile 2013 client and also using it against Lync Server 2013 only.
However if your user estate includes Symbian or Windows Mobile 7.X then you will need to continue to use cookie affinity also if you need to retain Lync Server 2010 whether in the short or to medium term.
Also keep in mind the release of the Lync Mobile 2013 client (when it becomes available) might not be released for all platforms at once.
But you can continue to use cookie affinity with Lync Server 2013 if you wish.
However cookie presence adds a layer of complexity with having to maintain the certificate on the HNLB so removing it (if your able to) is a good thing in my book ‘keep things simple’, but you might want thing about Blocking Lync Mobile on specific mobile platforms as well as earlier version which require cookie presence.
Changes in Lync Server 2013 That Affect Edge Server Planning
Hardware Load Balancer Requirements
Technical Requirements for Mobility