I always thought Modal Conditioning Cables (MCP) were only used to couple "single mode" transceivers to multi-mode fibers where you needed to drive the light further than the spec allowed.  So basically the transmitter physically connected to a single mode fiber strand, the MCP perfectly spliced/centered the single mode fiber to the multi-mode fiber and this allowed longer range over multi mode fiber.

Then I ran into this and this document.

The requirement for MCP is specified only for 
10GBASE-LX4 and 10GBASE-LRM transceivers transmitting in the 1300-nm 
window and in applications over MMF. MCP should never be used in 
10GBASE-SR links in the 850-nm window.

The Cisco 10GBASE-LRM Module supports link lengths
 of 220m on standard Fiber Distributed Data Interface (FDDI) grade 
multimode fiber (MMF). To ensure that specifications are met over 
FDDI-grade, OM1 and OM2 fibers, the transmitter should be coupled 
through a mode conditioning patch cord. No mode conditioning patch cord 
is required for applications over OM3

I must confess, I've deployed some 10GBASE-LRM over FDDI-grade and OM1/OM2 fibers and things work just fine without the MCP.  Do you only need it when you're pushing the 220 meter limit?

How many of you really use MCP to "ensure that specifications are met"???  Fess up.