When is the additional feature of DFC boards really necessary?
We're trying to trim costs these days. I'm not sure if our data center switches really actually require DFC. Is there a problem with over-subscription without the DFC boards on a 6748 blade?
We currently have a few 6509 chassis with 6748 blades installe. We haven't really experienced any problems.
Have a look at this Q&A which has a specific section on what benefits the DFC's give you.
Oversubscription is something slightly different. The 6748 blade is oversubscribed but not by much ie. it has 48 10/100/1000 ports with 2 x 20Gbps connection to the switch fabric.
Overall, if you are not experiencing problems without DFC then no need to use DFC. We had a data centre where most of the servers were not using DFC enabled line cards because they didn't need it.