I picked up the 7' hose because of a class requirement for stage-deco.
The reason given by the instructor was that when you are nose-to-fins inside of a shipwreck, and also sharing air(nitrox/trimix), you need it.
He had a strange way of curling up his long hose, which was yellow, and bungee-ing it near the top of his right twin tank. I instead read about the JJ-method of curling it around your torso from a book at another scuba store. [If you have never read JJ's book, it is worth doing; he has all sorts of interesting ideas, some of which are quite good, and others not always so good depending on the circumstances of the dive environment.]
I used the 7 ft hose for all subsequent diving, single tank or double tank, even with no shipwrecks in sight, because I wanted to get accustomed to having it all the time.
When you gear up with this, using the torso method, you need to tuck a portion of the hose into your BP belt. The procedure step in gearing up is worth getting used to. I like to do things the same way every time, when possible and safe [this is one of JJ's ideas too, although he does not qualify it like I just did].
For DPV diving, a 7 ft hose is also quite critical for air(nitrox/trimix) sharing.
So if anyone asks me, "Why do you have a long hose?"
Then I say, "Which hose?"
And they say, "That hose."
Then I explain about the DPV.
Then if they ask me, "Are you DIR?"
Then I ask them, "What does that mean? DIRRR?"
Then I will tease them about as many DIR things as they know.
My point then being, that whatever this DIR thing is, with its unfavorable reputation among ordinary divers, it does not mean that anyone with a long hose is unfavorable.