I got two complaints for MCR.
1. My boss has an IP set and a soft phone. Usually, he uses the handset of the IP set to receive calls. But if the call is too long, he will "transfer" to his headset of his soft phone. Such "transfer" can only be done by SCR.
2. My co-work's phone is very busy. Sometimes, he doesn't want to pick up an incoming call, but wants to make an outgoing call. With MCR, he has to wait the call CFNA to voice mail. With SCR, he can use his phantom line to call out in this case.