Would you recommend using these and with what sort of magnitudes, durations and targets? And while we're at it, what about blind, sound, reflect, spell absorption and shield spells. I'm asking about this, in particular for a nightblade character with 2.5*Intelligence in magicka. It doesn't sound very efficient, but if it is, it would surely make the gameplay more interesting.

Do you mean the flee effect? Because I have always found that to be quite pointless.

No, I mean the drain/damage/absorb willpower spells one finds on telvanni amulets. Although I'm suprised you'd find demoralise pointless; it's handy when you're out of your depth.

Oh those things. Well damaging/draining attributes can come in handy when it is strength, intelligence or even speed. Absorb strength is often just brutal.

Sound reduces the opponent's odds of casting successfully. Since the NPCs generally are designed so that casting their spells isn't a problem, Sound only gives a SMALL chance for them to fail. It's not like where the player-character has a 60% chance, and another 10% penalty is significant. Silence might work better, if you can afford to cast it for a long enough duration.

Most of the defensive spells (Reflect, Absorb, Shield) have such a high casting cost that you can only afford a small magnitude or duration, making them only semi-useful (although using an Enchantment, which won't deplete your own Magicka, could be handy). Sadly, Morrowind (and most of the rest of the series) makes it non-cost-effective to use magic defensively.

Small wonder they were removed in later games (it was either that or making them better value after all). I think it might be feasible if only the one school is used like a bard who uses illusion or a mystic monk, but for a nightblade, I think the bread and butter are invisibility, mobility spells, health absorption and a jinkblade in one's knife set.