I will give you an example.
I use SLEEPCYCLE app, which I switch on before I go to sleep and switch it off as soon as I wake up. Since SLEEPCYCLE only makes a small dent in battery drainage, I used to get a usage of 10 + hours daily, and this used to confuse the hell out of me. For a while, I thought iOS 8 has improved battery life dramatically.
I started a thread, proudly wanting to show off my great battery life, until some other members on here, pointed out to me that using apps like these add to your USAGE hours, without killing the battery. So yes it is misleading, and I felt a tad bit foolish...
Now, as long as the phone lasts me a day (which it does with about 20% still left by the time I reach home), I have stopped looking at the usage and standby..