Canceling SQL Server Support
(By support I'm assuming that you are talking about software assurance.)

SA gets you two basic things.


Phone Support
Ability to upgrade


It also gets you some other stuff.

If you have a cluster and you have an Enterprise Agreement then you get something called license mobility which allows you to have a passive node for free.  If you aren't clustered but are running within a VM license mobility gives you the ability to move the VM from host to host without issue.  If you don't have license mobility then you can only fail over the cluster (or move the SQL VM from host to host) once every 90 days.

Given that Microsoft is moving to a short release cycle (18-24 months give or take) having SA makes sense if you plan on upgrading any time soon after the new version comes out.

Now if you don't care about that stuff and you ditch SA you can still call in and get support for SQL Server, but keep in mind that you'll be the last one in the queue to get a call back, and at the lowest priority.  Now if you never call support that's fine, but when you do having SA in place pushes you up the chain from level 1 support to starting at level 2 support.

Now given that you are on SQL 2008 R2 today if you ever plan on upgrading to SQL 2012 or SQL 2014 if you don't have software assurance you have to purchase all new licenses to upgrade using the new licensing model.  If you have software assurance you get to upgrade for free.  So if you are using SQL 2008 R2 standard edition CPU licensing today a SQL 2014 upgrade might be really expensive all of a sudden due to the core licensing change which started in SQL Server 2012.