I was thinking about the whole concept this last weekend as I was visiting my mum. Forget balancing on a Bosu ball or single leg deadlifts...I saw what was important. She is 77 and has now got rid of the bath for a walk in shower because she was no longer able to get in and out of the bath. She walks... but it is getting harder. Standing up from the floor? I don't know if she could.
That is the sort of function that we need. Sufficient strength and appropriate skill to survive independently, to live independently. All of the endless debates and arguments about training methods frustrate me. Just get stronger and do it safely. Take the long view. Is what you are doing something that you can keep doing for the next 40 or 50 years and will it give you the strength and skills to be independent when you are 70, 75, 80 or more?
And the bigger context of course is death. No matter how functional you are death is coming; strength will help make your life more fun and easier but it is not the whole story. Strength will let you function, but what are you doing with those years?