One could easily decide to eschew either undead or daedra and focus only on one category of summon, as another example.
Yes, one of my active characters is like this. She's a Master Conjurer/Illusionist, but she hates Necromancers. She has never summoned any undead, but relies heavily on her Daedric summons, because she is an Altmer with the Apprentice birthsign, with starting-level Endurance, and cannot stand up to direct magic attack. Her usual practice is to summon her daedroth or xivilai to draw the aggression of the enemy, and then to stand back and cast paralyze to make her helper's job easy.
I think that most of my characters have been primarily two-skill fighters... Restoration pairs with almost anything, and even substitutes for Destruction in close-in fighting (Absorb Health.) I pair it with a melee skill for the head-knocker type of character.
Alteration pairs well with Illusion. A well-shielded caster who can disappear at will, Silence enemy casters, Command enemies to kill each other, and Paralyze the last enemy standing.