Aside from the Werewolf power.

Why are powers that are once day either are terrible to use or just have no use at all?

Is this Bethesda's way of giving players a sample when it comes to using spells?

There just little beginner powers to help new players out. Far as I feel about em they have been powers that quickly get over shadowed by better skills since Morrowind.

They might function as an intro to spellcasting, sure, but they are also a way to reflect cultural distinctions- Bosmer can command small animals, in keeping with their history; Imperials have the innate ability to "calm" people once a day, reflective of that culture's "knack" for diplomacy, etc. A primary draw of racial daily abilities in the earlier titles was that you could rely on them to work. They would never fail, unlike spells. In Skyrim, there is no spell failure, so the daily powers seem less useful.

As for how powerful those daily abilities are, I have never really worried about that. They are tools, not crutches. They are typically helpful early on, and that is enough for me. Some daily abilities stay useful, such as the Orc's Berserker Rage, but that doesn't compel me to play them more often.

I wouldn't know. I keep forgetting to use them.

There are many useful daily powers. Secret of Arcana lets you go wild with your magic spells without having to rely on a bunch of enchantments. Histskin will save your life. Mora's Boon does the same, but also restores magika and stamina. The Ritual Stone is great for raising an army of the undead to attack a particularly tough opponent. Spectral Assassin is a ghost follower.

Though I have the same problem as Pseron. I keep forgetting they are there, and when I remember I keep wanting to hold onto them just in case I need them a little later.

That's my trouble, too. I keep "saving" them for that "tough fight" that rarely appears. When it does, I totally forget about them