This prohibition is designed to protect the neutrality with which officials should act, that is, avoiding situations in which a conflict of personal interest of the person elected and the area of decisions for the public interest he may be involved in could arise because of his position. This could include decisions on the renewal of certain concessions, decisions regarding which company a public service or contract should be awarded to, urban reclamation of land in which a land owner or a contractor elected as mayor may intervene, etc.
Examples incorporated constitutionally are abundant.