A bit has been said about visitations.  Protestants don't have wakes, so the visitation is in lieu of that gathering.  For most families, there is only one night of receiving guests now, although it varies by culture, location, family, and funeral home. 
I can see the long night, usually the night before the funeral, when long-time friends flock to see the grown children that have moved away, and to show respects and speak to them before the crowds at a large funeral might preclude the chance to speak.  I've seen many a state room filled with laughter and hugs and a reunion atmosphere, and was so happy to see a sad occasion turned into quite a bit of joy.
It not necessary by any means, but often the day of the funeral, family members may be devastated, even when the death was long anticipated, as putting one's loved one into the ground is emotionally very difficult for some people, and you don't want to rush forward and offer condolences when people just want to get away and back home to grieve in private.  
Fortunately for my immediate family, Grandmother's death was overdue, and scattering her ashes on Granddad's grave was not sad in the least, and we even had a good laugh as her dust blew into my pants cuffs, as she was always untidy as a housekeeper.  
 
But, when Granddad died some 31 years earlier, it was sudden, and unexpected, and Grandmother, who was normally the picture of composure, was deeply shaken.  So, I've seen both.