[Sed - An Introduction and Tutorial by Bruce Barnett](http://www.grymoire.com/Unix/Sed.html) has this in [The essential command: s for substitution](http://www.grymoire.com/Unix/Sed.html#uh-1):

> 
> A simple example is changing "day" in the "old" file to "night" in the "new" file:
> 
> 
> 
> ```
> sed s/day/night/ <old >new
> 
> ```
> 
> Or another way (for UNIX beginners),
> 
> 
> 
> ```
> sed s/day/night/ old >new
> 
> ```
> 
> 

What is the difference? Why does Bruce Barnett specify that one method is "for UNIX beginners"?

I can see that `old` is being used as input in both situations, and I can see that `new` is being used as output in both situations. Does the extra `<` make any difference?