Assalamu alaikom wa rahmatu'lLahi wa barakatuhu,
Sahoor is a sunna that our prophet Muhammad Salla Allah Alaihi wa Sallam did when he fasts.
Inshallah our fast will count without it BUT we should have the Sahoor whenever we fast. There are multiple hadeeths with different reporting about it, there is " baraka " (+/- blessing) in it. And we should have it even with one half of a date.
A common mistake that muslims are doing specially in Ramadhan is that they eat a lot very late at night, before sleeping considering that was the Sahoor but it is not, Sahoor should be right befor the Fajr Adhan. There is also a hadeeth about it meaning that the islamic ummah (nation) will be alright (+/- healthy, good) if we delay the sahoor (we sleep then wake up to have it right before the Adhan) AND harry with the iftar (breakfast at sunset just after we hear the first words of Adhan (not after the muadhin or caller for prayer says " la ilaha illa Allah " another common mistake ! )).
Wa Allahu Aalam.
Assalamu alaikom wa rahmatu'lLahi wa barakatuhu.