I have often wondered about this practice. I've read about it in novels and seen it in movies, but I have never heard an explanation about why people "sit up" with the deceased round the clock until he or she is buried. Does anyone know why people do this?

I think that the purpose of a 'wake' or sitting up with the deceased came from the days when death was not so certain and the 'corpse' came back to life, having only been unconscious or in a comatose state.
They didn't want to accidentally bury a live person so they stayed 'awake' until it was obvious that the deceased was really not coming back.

In the area of the United States where I grew up [that being east Texas-Louisiana ]it is still widely practiced and is actually a great source of comfort, in many cases. There is generally a big party and lots of food. At my aunt's funeral near New Orleans, all her friends and loved ones were encouraged to bring favorite photos,childhood drawings or anything else near to her heart and lay them with her in the casket. She was still fairly young and her death untimely...it really helped her children and grandchildren to face her passing with a "send-off" rather than a more staid funeral.

It sounds a bit morbid but I enjoy funerals. In Australia, for some religions, after the serious and saddening part of the service and graveside/crematorium, a lot of the mourners will go back to a family friends house and pay their respects to the members of the family.

That's when the enjoyable part starts. It's a chance to catch up with relatives and friends you have lost contact with and never would have seen if the relative hadn't passed away. It's equivalent to a family reunion and great to find out what everyone has been up to over the last twenty years. I think it sort of takes a lot of the pressure off the previous events of the day.

Like you're accustomed to, Exit10, we in the southern United States also have family gatherings after a funeral. That's usually the only time I ever see great-aunts, great-uncles, and second and third cousins!

However, I guess my question was answered by fjohn. That seems to make sense, since in past centuries the medical technology wasn't available to "make sure" someone was dead and not merely in an extreme comatose state. Thanks for the input.