Depends on what type of

Depends on what type of teaming you do.  I don’t recommend link aggregation (teaming) cards unless they are the same chipset though.  You can go for reliability or performance.  With teaming you’ll have less overhead (CPU) per card and more throughput.

See http://support.dell.com/support/edocs/network/9195p/en/Intel_nic_teaming_10.pdf for a good whitepaper on teaming.  It is old but the core concepts are still valid.  It includes a table on performance.

I only have network cards team on my routers, file server and dev box.  On my HTPCs I don’t and don’t see the need for it.