There is a lot of virtue in performing the sunnah muakkadah. Even if there is not a torment of Hell when they are abandoned intentionally or out of laziness, a big loss such as being deprived from receiving Prophet Muhammad’s (pbuh) intercession (shafa’ah) is in question. Such people deserve being condemned by Prophet Muhammad (pbuh). Altering or denying sunnah muakkadah is bidah (invention in the religion) and going astray.
There is a lot of virtue in performing sunnah ghair muakkadah (acts and deeds Prophet Muhammad –pbuh- used to leave sometimes) too. We can turn our daily activities such as eating, dressing etc into worship if we do them in accordance with sunnah. This way, habits become an opportunity to receive Prophet Muhammad’s (pbuh) intercession. Even applying the smallest item of the sunnah makes us remember Prophet Muhammad (pbuh) and gives peace and light to our heart. There is not any type of punishment or condemnation in abandoning the second type of sunnah. However, there is the situation of loosing big opportunities and not being able to make use of the light of sunnah and true high ethics.
He who abandons sunnah also abandons the true high ethics, and it brings about deprivation from our Creator’s favors.