Useful in any situation?. I have yet to use these in any game so far

They are extremely useful if you ever need to banish/command/expel daedra. In other situations these skills are worthless.

Are there any fixed encounters they are handy for?

Conjurers rarely bring out daedra. They mostly prefer raising dead people.

One fixed encounter is the standing stone northeast of Whiterun. Almost directly NE from the Battle-Born farm.

However it prefers to reanimate the nearby skeletons.

Keep the spell though because it will be a life saver when you do face those power conjurers that decide to bust out with their own. They also WILL use Command Daedra and turn your own summon on you. Expel will be very good for this.

As a heads up, Expel Daedra is not very strong, it can fail sometimes if the daedra is high level.

My preference for Expelling is a Perked Bound Weapon, because it is a level 99 Spell. Command Daedra is useful for Conjurers/Justiciars/Dragon Priests that like Atronachs, even if Terra Nova is correct about the Spell being used by Them on Our Summons.