elemental summoning tactics

With high spellcasting skill, a significant number of elementals are summoned (4x spellcasting on expert difficulty). But in practice, I don't remember any situations where the summoned elementals were decisive.

I've had it happen a few times on custom XL maps, where towards the end of the game, I ended up in an elemental battle with the AI, but the heroes there also had all their stats at 50+. So it was a tough fight....
But it would be interesting to simply learn from experienced players in what situations they use the elemental summoning spell...