Shared transport directory best practices?

Does anyone have any documentation / knowledge on using a shared transport directory - ie, BI, R3, SolMan, etc in the same '/usr/sap/trans/cofiles + data directories, or is it preferred to keep them separate?

Currently, our R3 system shares one transport directory across the landscape, but BI, SRM, and Solution Manager do not. While thinking about giving each of them their own shared directories (all BI systems share a directory, all SRM system share a directory, etc), I wondered if the preferred method is to have them all share a directory.

I would appreciate any input, thank you.

~TJ