Is there any harm in abandoning the sunnah prayers performed together with the obligatory daily prayers?

The regular sunnah prayers performed before and after the obligatory prayers are divided into two categories: mu’akkad (emphasized) and ghayr mu’akkad (non-emphasized) sunnahs. A mu’akkad sunnah is a practice that the Prophet (peace be upon him) performed regularly, but occasionally omitted to show that it is not obligatory. A ghayr mu’akkad sunnah is one that he sometimes performed and sometimes left. Ghayr mu’akkad sunnahs are also called mustahabb (recommended). It is not proper to abandon the mu’akkad sunnahs without a valid excuse. Abandoning them without excuse is considered ‘isâet’, meaning a wrong or faulty action; however, it does not incur punishment. As for the ghayr mu’akkad sunnahs, they may sometimes be omitted even without an excuse. (Ibn Abidin, Radd al-Muhtar, 1/103-104, 474, 478)

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu