Why is Surah An-nas, Surah Al-falaq and Surah Ikhlas important?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. May Allah guide us and you to the right path. Know dear brother, that all the Qur'an is important because it is The Guidance, The Cure, The Admonition and The Blessing. As for the Surahs in your question, their preference is mentioned in several Hadith. Muad Ibn Jabal (Raliya Allahu Anhu) narrated from his father that he said: "Once there was little rain and much darkness and we were waiting for the Prophet (Sallallahu Alaihi wa Sallam) to lead us in prayer. (He then said something which means): then the Prophet (Sallallahu Alaihi wa Sallam) came out of his home to lead us in prayer and said (to me): "Say" I replied: "What do I say". He then said: (Surah: 112, 113, 114)" [ Ahmad and al-Nasa'e ]. Abu Said (Raliya Allahu Anhu) narrated that: "A man heard another man reading Surah 112 and repeating it. The following day he mentioned that (what he saw) to the Prophet (Sallallahu Alaihi wa Sallam), thinking it was of little importance. The Prophet (Sallallahu Alaihi wa Sallam) said: "By whom my soul is in His Hand", this Surah (112) is equal to a third of the Qur'an" . Abu Said (Raliya Allahu Anhu) also narrated: "The Prophet (Sallallahu Alaihi wa Sallam) used to seek refuge with Allah from Satan and evil eye of people until the Surah 113 and 114 were revealed. Then he recited to them and gave up other incantations. Allah knows best.