system
Given the following post, respond as if you're commenting on Reddit:
human
[Sandman] if the Endless are single entities that do one thing at a time, how do they affect all humans?

We see Death bringing...well, death to people. and doing the first phase of bringing people to the afterlife. We see her do this as a single entity that does only one thing at a time just like a regular earthly mortal animal would. Her actions, movements and thoughts move at human speed. 

So how does Death kill all the people it kills at once and is everywhere when she is not?

How does Morpheus bring sleep and dreams to all the humans that are sleeping at the same time?
gpt
We know Morpheus visits individual peoples dreams but also delegates much of his work to others (the Corinthian, Fiddler's Green, etc). There's enough infrastructure and support in place that the dreaming continues even in his absence (albeit slowly decaying). 

Presumably Death's operation works the same way. She handles some cases herself, but has enough support to tackle the whole volume without her individual involvement.