[Translator Reform] Fill-ins: Why is the proposed reserved band fill-in translator rule necessary?

NOTE: This answer relates to a rule proposed by REC and does not reflect current regulations in effect:

This rule is necessary to assure that NCE stations, especially smaller stations are able to grow their signals into nearby communities without the concern of all opportunities being precluded by well-established NCE stations in more urbanized areas proposing fill-in translators for the purpose of HD rebroadcast. The fillin service was originally designed to help NCE FM stations fill in holes in their primary coverage areas due to intervening terrain or other obstructions. Fill-in translators are not used much for that purpose anymore.