You may want to place two lines together in your
presentation but, please don’t underline text!
On the whole, I couldn't agree more. Underlining is a throwback to the bad
ol' days when we used typewriters. They couldn't do italic, so we
underlined stuff as a way of saying "If we could set pretty type, this would
be in italic, but we can't so we'll just have to settle for this ugly
clutter."
But: in accounting/finance, the double underline indicates a total. It
actually has a meaning rather than being a standin for something else.
Sometimes it's necessary, in other words.