ADVICE: Sunnah Salahs/Prayers Can Benefit

It was narrated that the Prophet Muhammad (SallAllahu 'alaihi wa sallam) said: “The first of his actions for which a servant of Allah will be held accountable on the Day of Resurrection will be his prayers. If they are in order, then he will have prospered and succeeded; and if they are deficient, then he will have failed and lost. If there is something defective in his obligatory prayers, Allah will say: ’see if My servant has any supererogatory prayers with which may be completed that which was defective in his obligatory prayers.’ Then the rest of his actions will be judged in like fashion.”

 [At-Tirmidhi, Abu Dawood, an-Nasaa‘i, Ibn Majah and Ahmad]

ALLAH KNOWS BEST.

A Muslim who prays the five obligatory salahs is much better than a person who does not pray at all.

A Muslim who prays the Sunnah/voluntary salahs before and after the obligatory salahs is much better than a Muslim who prays only the five obligatory salahs.

A Muslim who prays the Sunnah/voluntary salahs before and after the obligatory salahs AND regularly prays Dhuha in the forenoon and Tahajjud at night is much better than the Muslim who does not regularly pray Tahajjud nor Dhuha.

The similitude of the above is that of students who received different grades in an exam:

a student who got a C for his mark is better than a student who got an F

a student who got a B is better than the one who got a C

an A student is better than a B student

and an A+ student is much better than an A- student. 

As humans we cannot be sure that every one of our salahs/prayers, since the time we are held accountable, are accepted 100% so in order to compensate for the 'unaccepted' salahs, it is encouraged or even necessary to pray as many Sunnah prayers as you can every day and night.

Allah knows best.