Intrigued by this discussion . . .
When I was flying around fairly flat terrain at sea level for a good, early part of my career, thinking about power available vs. required didn't get the focus it should have.
I learned real quick just how important it is to be "on" this at all times when I started flying mountains and landing Robbies at 7,000' D/A. I have come across instructors in mountainous terrain who prove power available prior to an approach and do nothing to assess power required. This bothers me greatly.
When I started flying mountains I knew I needed something off the top of my head to assess whether I could go and do stuff or not, and it bothered me that maybe I had to refer to charts because I knew this would be rather impractical in the aircraft.
Very similar to Brian Abraham's 205 rule of thumb, which I like a lot, it goes like this: work out how much power you need IGE when you are first skids-off and make a mental note. On your climb out level off briefly at 500' AGL & best rate of climb speed. Note the power REQUIRED for S&L flight. The difference between the two - the power margin - is key here.
Now, you've arrived at your intended landing site, and it may be higher, hotter, windier or whatever. Fly past 500' above the site at best rate of climb speed noting power required. Now pull maximum power available and note the value. Determine the power margin and if it's equal to or greater than the one you assessed on take off and climb out from your departure point then your chances will be pretty good. If not, go and land somewhere else after repeating the procedure relative to the new landing site.
The thing I like about this is that you can take it out anywhere and it's so simple.
I also agree strongly with SAS . . . power assurance checks are fine to prove the engine is doing what it was designed to do. What's necessary is establishing that what you want to do is possible at the time you need to do it. It's absolutely possible the engine will perform as specified and the heli will not have hover capability, so working out what you've got and comparing this to what you're using is critical.
GP