Got a bunch of them on scrolls from the magic shop in Silver Blade. Tried one out and I don't understand what the hoopla is all about. I can't think of an instance where I'll need a fireball to not explode when I cast it. Is there something later in the series where a delayed explosion is desired?

The main advantage is it can affect enemies who are immune to normal fireball (for example enemy mages with Minor Globe of Invulnerability pre-cast)

Thanks, haven't experienced that set of circumstances yet. What about the whole delay thing? I'm still trying to wrap my head around a possible need.

I never found an usefulness for delaying the blast in any gold box game.

Yeah, the delay is useless.

The other reason Delayed Blast Fireball is better than Fireball is that it casts instantly. (Most spells take [level/3, round down] segments to cast. A 7th level spell like DBF would normally take 7/3=2, but takes 0 if you don't add a delay. Standard Fireball takes 3/1=1.)

IIRC Delayed Blast Fireball deals 1d6+1 damage per caster level while Fireball is 1d6 per caster level.