the idea is that you want the mobile to camp at the cell where you want the conversation to be. for example you camp on a loaded cell in idle mode. the mobile originates a call – but you set the traffic to go to neighbour and => handover. Incresed risk of call drop etc.
CRO can be zero of course but it could happen that you change very often between cells on borders, and neihgbour list changes etc. It’s just a hysteresis.