After multiple repositories (BAM-1868 BAM-955) / multiple modules per plan (BAM-1015 BAM-1211) is implemented, the builder will have to cope with the situation that more than one directories in the sand box contains the POM - in a frequent scenario one of the directories will be the parent module and the other will be the actual module that needs to be built. It this situation is necessary that the correct POM can be selected during plan creation.
The change would be backward compatible - not entering POM location would result in POM lookup performed in the same way it is done now.