First - you cannot enable or disable auto-summarisation on routers.
You can configure Cisco routers as 'classless' or not - implying that they understand that prefixes are independent of any class-based structure (A,B,C).
Auto-summarisation is a function of a routing protocol. The simple answer to the question is NO it is NOT a good idea disable auto summarisation. (Oh, I can hear the techies jumping up and down at that).
Reason? with no other contributing factors except the question as to whether it's a good idea, the only possible response is No.
But the 'fully-qualified' response is this... if your network and network-population is addressed in a proper Classful manner where all networks are contiguous, then there is value in having routing protocols configured to perform auto-summarisation.
But there are most likely no networks that look like that. And as soon as you do break a natural network, you now have multiple natural summary's floating around your network pulling traffic in different paths to different destinations. Not a good situation.
It's a big question with a lot of the base elements of good IP address structure at its core. You should go read all about CIDR, and understand the differences between a prefix, a network and a subnet.
peter
