For example, LT-1 powered 4th Gen Camaro's use a pull type slave cylinder with a clutch fork while the LS-1 powered 4th Gen Camaro's use an integrated throw out bearing/push type slave cylinder. Therefore swapping an LT-1 T-56 tranny into an LS-1 powered car may not be legal even though the cars are on the same line (there's other reason's this wouldn't be legal such as having to change the LT-1 tranny input shaft to an LS-1 input shaft).

I know that doesn't answer your question as to why it's there, but here's an example of what it does prevent.

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MLS Motor Racing

It was there from the C4 corvette BSP corvette days, maybe even pre LT1 motors.  One of the trick clutch setups required a switch from pull to push style actuation.  At the time that was considered too much of a change for SP, and no existing wording was there to make it clear.