All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
From the Sharee’ah point of view, the Sunnah means the Prophet's sayings, doings and sanctions. According to the above meaning, the Sunnah includes obligations as well as recommended and desirable actions.
So, saying it is not necessary to follow the Sunnah constitutes a big blunder, since the Sunnah is the second main source of the Islamic legislation.
In Fiqh terminology, the Sunnah is more specific than the Sharee’ah meaning. According to the jurists, the Sunnah has a lower degree than obligation, but one higher than what is permissible and desirable. In this specific meaning, it is right to say: 'One who leaves out the Sunnah is sinless'. But, a Muslim who desires to receive the Divine Mercy and then enter Paradise, should not leave out the Sunnah voluntarily since Allah Says in a sacred Hadeeth: “My servant keeps on coming closer to Me through performing Nawaafil (optional deeds) until I love him.” [Al- Bukhari]
Allah knows best.