You do this because you end up seeing messages in the health analyzer about databases not upgraded (you open it because your site stopped working): "The following databases have versions that are older than the current SharePoint software, but are within the backwards compatible range: User Profile Service Application_SocialDB_c364a011f36f4e9ba210bed78f964665, Search_Service_Application_AnalyticsReportingStoreDB_89dd14f5835d4d368b8912cb2ff2d17e, Bdc_Service_DB_29ef5f7ce1d14088bfbd5d63223872a2, SharePoint_Config_f82eb164-7374-435a-b987-c1766e914af3, AppMng_Service_DB_556cc2d02a9140e7887ed67db619001f, SharePoint_AdminContent_51fce7bf-6f79-45db-9682-fd7a104839ad, WSS_Content_318a3672-b982-4b1e-bc54-4181dfd3f8c0, Search_Service_Application_DB_cd636bd8e1d149f19dfcfba6b27937ae, User Profile Service Application_ProfileDB_cdd94abe9d66468685df50e618f0564f, WSS_Logging_4b6ad66f-2b8c-4e6f-9264-acba62dcc35b, Search_Service_Application_LinksStoreDB_b48f5e42753d4600a0ec6eb62e1602a9...