When a candidate applies they add their address, currently in v3 quick apply this is one address line + postcode + county + town.
As a default cascade maps address from the candidate account fields (unless changed in configs) this results in address line 2 never being mapped to (unless changed to be driven from a sup form field).
Hayley raised this could become an issue in the future as address line 1-2 are required in one of cascades integrated payroll systems.
There is a work around for this however I've seen on older v2 quick apply apps address line is split.