Before 5.0 the intent was that DS won't heal unless it hits. Even after 5.0 GC said something on the lines of "tanks should need hit/exp for their survivability tools, not for their dps tools" meaning that it's ok for a tank to miss with a dps ability, but shouldn't be ok to miss with a survivability tool.
We could argue that hit/exp doesn't do enough for us. It's also down somewhat to personal preference. Fight mechanics (mainly damage patterns) make a huge difference about just how important/useless hit/exp capping is.