ClearanceDist is a track parameter that indicates how far along the diverging end of the switch must be clear on both tracks for the switch to be clear.
If this distance is too short then a signal will indicate clear even though both tracks are not clear. This can result in a collision with a traffic train that starts when the signal clears.
If this distance is too short and their is a signal closer to the point than the clearance distance this can result in a signal passed at danger (SPAD).
Since Route Editor does not indicate when a signal is within the clearance distance of a switch both problems are difficult to avoid.