Man of Honour
Actually @Angilion makes a good point. Unless you're carrying PA parts in your inventory that perk does seem pointless. Unless of course it reduces the weight of the power armour chassis? I could see the appeal to that if it could be reduced down to say 2Ibs.
The Portable Power perk at rank 3 reduces the weight of power armour parts and chassis by 75%. So it reduces the weight of a full set of equipped power armour from 10lbs to 2.5lbs.
I could see some appeal if perks didn't use stat points. You only ever have 56 stat points. Using 3 of them to lower your carried weight by 7.5lbs seems unlikely to be the best use of them. Even worse, you can only ever have a max of 15 perk points in any one stat (you can go over 15 in the stat with bonuses, but you can't use the points over 15 for perks) so you're even more restricted. I spent at least an hour trying to fit the build I wanted into the stats I could have. I started off needing 29 perception points alone Nukes Dragons has an excellent FO76 build planner.
So for the cost of 3 int points you reduce your overall carried weight by 7.5lbs. But that's 3 points you can't use for another perk. You could, for example, use just 1 point in strength and take 1 rank of the strong back and gain 15lbs carry weight (5 for the str point, 10 for the perk), i.e. much better than reducing your carried weight by 7.5lbs and costing 2 points less. Even if you've taken 15 int points (and thus skimped on some other stats and perks) and even if you're totally fixated on power armour there are still better options. You could swap some of the int perk cards in and out and make do that way, I suppose.
But in the end, why bother with that 7.5lbs anyway? You'll be able to carry at least 185lbs in power armour and that's assuming you put no points at all into strength and don't use the excavator armour and don't use the calibrated shocks mod (which adds another 100 to carry weight). My walking around load is about 100lbs and that's including carrying food, water, ludicrous amounts of ammunition (~1100 .45 and ~1100 shotgun shells), rad-x, rad-away and stimpaks. Oh, and a sword just because. And some clothes. And a hat. And sunglasses. And lined underarmour. And a couple of dozen strangely heavy bobby pins. I think Bethesda mistakenly set the weight of bobby pins to be 10 times what they intended.
On the plus side, I got the "Falsely Accused" quest dropped on me this morning and when I went to the penitentiary to do the quest the scorched swarming the jail were unusually well armed. About half of them were carrying a combat shotgun or combat rifle. So I learned enough mods to make both viable and could retire my pipe revolver and pump action shotgun. The combat ones do quite a bit less damage per shot, but the fire rate is much higher so the DPS is much higher. The combat rifle is bugged, by the way. The full auto receivers get the bonus from the non-auto rifle perks and I think the semi-auto receivers get the bonus from the full auto rifle perks. I didn't want full auto, but with my non-auto rifle perks the powerful auto receiver does more damage per shot than the semi-auto receivers I have (I don't have the hardened receiver yet). Something to look out for if you use combat rifles.