To attempt to answer this question, we need to put together a couple of elements.
First, what does HIVE Power (HP) offer?
Of these benefits, which are transferred by HP delegation?
On the interest part, I am not sure, but I know others know the answer to this. Have you noticed that if you delegate HP to someone, that amount in HP grows over time?
For example, I delegated 5,000 HP to 
We know that HIVE operations at the core of the blockchain use the VEST token, which is for internal use. That means that internally, you delegate VESTS to another account, not HP. We also know that the ratio between VESTS and HIVE fluctuates. If the delegation remains constant in VESTS, that means the increasing delegation in HP happens only because VEST becomes more valuable over time compared to HP. Don't ask me to explain exactly the mechanics behind that, I'm not that knowledgeable about the inner workings of Hive.
So, one way or another, the delegation increases in HP over time. I choose to think (although I don't have knowledge or evidence in that sense), that interest plays a role in that increase.
So, in my interpretation, ownership for interest paid on delegations remains to the delegators, but it is used by the delegatees until the delegations are withdrawn.
Owners also retain the full governance voting rights, as we know.
So, if we were to synthesize, a delegatee (often a big project if we are talking about worth) often uses a delegation in one or more of these ways:
Also, if we are talking about projects and not individual delegatees, they often offer some incentive to be delegated HP. There were also options to lend HP for an APR to whoever was interested in delegating their HP out. Not sure how many of them still work.
The rewards/incentives one receives in return for a HP delegation are very important to analyze. The risk grows considerably the more exotic they are. As a rule I have for myself, if I don't want to accumulate the tokens received as rewards for delegating HP, it's not worth analyzing any further, regardless of the APR.
One could also say, simplistically, that the APR of delegated HP is 8/9+3=11/12%. So, a 15% APR would be enough to attract the delegation, right?
Well, in my opinion, no.
For big projects, rewards they can distribute from the reward pool is a bonus, but there are other things at stake:
For the delegator, there is also the matter of receiving second-layer (side-chain) tokens instead of the base-layer rewards. In most cases, this in itself should come with a premium.
In my opinion, the worth of a HP delegation is at least 20% (without conditions), unless rewards are also HIVE, in which case, it can be lower. Can be much higher for more exotic token rewards.
I haven't put a number on the worth of my HP delegations until now. It will offer me some strong guidelines going forward.
Today is also LPUD and I powered up 150 LEO:
