calendar now_to_universal_time/1 vs. universal_time/0

[Ryan Zezeski]

What is different about these two functions?  The only thing I can gather
from the docs is that universal_time *may* return local time in certain
circumstances but now_to_universal_time will not.

In my applications, thus far, when I need UTC time I've been using
universal_time.  Is this correct?  Should I use now_to_universal_time
instead?  I ask because I've been going through the rebar source code and it
uses now_to_universal_time.

-Ryan