Why two billing types RE and G2?

In VOFA, I compared billing type RE with G2, I donot see any differences, apart from description. Then why can we not have only G2 or RE?

Currently in standard SAP we have u2013

CR --> G2

RE --> LR, RE --> RE

With this change, in SAP we would have u2013

CR --> G2

RE --> LR, RE --> G2

Thank you for your help!