They are really just for extending pixel signal distances rather than injecting power.
If your looking for a "high voltage" style power distrubution system, you could send 48VDC around your yard and use step-down regulators to pull it back to 12VDC/etc where required. I looked in to doing this but due to the regulator current limits, it's been just as easy to run thicker 12VDC cables everywhere to begin with. But for lost of small elements with 1A current draw each - and long distances between - i step-down system could be more cost effective.
I use the PPI in my P12 and PPD system. In cases where I have more than 25 nodes on an element, I use the PPI to inject power into nodes 26 and beyond. At this time, I do not have any single element over about 55 nodes and this is working well for me.
My source voltage is 36v and my nodes are 5v.