Nah...
Counterarguments (some are quite weighty)
1) We won't be able to research Eagle Eye and what's behind it!
2) We won't be able to research Magic Affinity!
3) I almost never have enough Dark Energy to raise all the suggested creatures during the week!!!
Even if we believe the manual, and it sometimes lies or omits something :) , we get the effect:
Health of raised units = Health of killed units * Necromancy, dark energy is spent on creatures. That is, since there is not enough to raise them, sometimes quite a lot, we will get that the health of raised units has an upper limit. Let it be 50. We fought 10 battles. We killed 200 HP in ten battles. Even with a developed Necromancy, we can raise (with a large amount of Dark Energy) 60 HP, with Death Lord 70 HP, but the limit is 50! We will not raise more than 50 HP (we are limited by Dark Energy).
Even in the late game with 4 developed heroes, when a bunch of undead are raised in grand battles, we will not achieve the result, because there will already be huge armies, but they, because they have a huge amount of HP, will be raised according to the scheme described above.
For me, the Graduate perk is even more useful than this one...

What is the beauty of it then?
P.S. I would like to understand the position of antonag07. Maybe it will help my gaming experience, but as I noticed (for now, IMHO, unless I am convinced otherwise), it is useless if you are not striving for Soul Armor.

Of course, Dark Energy runs out quickly both in the first week, when the hero is just starting from level 1, and in the later stages of the game (I usually run out of it no later than the third day). The point is to use it (Dark Energy) as efficiently as possible. At the start, skeletons are our main force - ideally, it would be good to immediately convert all Dark Energy into simple skeletons (by killing, for example, peasants or goblins), and then you can upgrade and start dealing with more serious neutrals. Without Necromancy enhancers (pillar 10%, "Death Lord" 5%), we will raise only 8 skeletons from 55 peasants. And don't try to convince me that you will have the opportunity to fight dozens of battles with neutrals suitable for converting into skeletons during the week - most often you have to beat everyone подряд (and raise everyone подряд so that the Dark Energy points don't go to waste).

Of course, "Magic Affinity", "Uncover Secret" and others also have many advantages, which are often more significant than the increased raising of skeletons - however, this option is quite viable even without the "Amulet of Necromancy".