I am a little confused. Seems by default most interfaces on a router are set for fast switching. What is the difference between cef and fast switching.
What do the following commands do:
ip route-cache cef
Why would you not want cef/fast-switching?
In short, route-cache keeps a traffic-drive cache of most used destinations, that is aged periodically and doesn't really take much memory. CEF instead builds a table for all the destinations using prefix-based algorithm (Patricia trees) that you can search about.
The reason you disable that, is because certain features (less and less, but still there are some) don't work unless you do that and fail silently.
Hope this helps, please rate post if it does!