Proper use of Eidolons?

[Telefrag]

Aside from instant healing and reviving what are the best use of Eidolons in fights? They seem to deal decent damage and build chain gauge pretty quick, but as soon as Eidolon expires every chain gauge and even active staggers resets which really makes me question spending 3 TP on summoning. So when it is best to summon an Eidolon?

[tiornys]

FFXIII's Eidolons are at their best against large groups of disruptive enemies/enemies with dangerous levels of spike damage output.

1: Summons cause any incoming attacks to miss, they heal you upon arrival and departure, and they cause more attacks to miss when you Gestalt.
2: Two of the Eidolons act as Sentinels. All but one of them will cast Curaga on the summoner whenever that character drops into yellow HP. All of the Eidolons will revive the summoner if they happen to get killed (although this will also cause the Eidolon to depart).
3: During Gestalt, enemies take no actions.
4: The combination of these allows you to deemphasize or ignore defensive measures when planning to Summon.
5: Therefore, as long as the Eidolon can output reasonable damage--which is doable but requires chain duration and sometimes chain building before Gestalt--using a Summon can be more efficient than normal fighting thanks to the ability to ignore defensive measures. As an additional advantage, Summons are inherently safer.

This vid demonstrates these principles on some random (not plot relevant) battles from chapters 7-11:

https://youtu.be/9EFkCgIQfck

Also note that if you skip the gestalt stage, you can prevent the enemy chain gauges from resetting. Depending on your plan of action, that's sometimes what you want to do. Here's a low development Adamantoise kill that exploits this (along with other things that Eidolons do to 'toises):

https://youtu.be/34t_tVpfvSY

[Telefrag]

Wow, that was really helpful! Especially the vid about avoiding stagger reset. Thanks a lot!

[Syad]

their high summon cost makes them situational and requires capability to play without them, and if you can do that, there is no need for eidolons. Even if they were the i-win button, which iirc they are not.

[tiornys]

You can generally Summon every 2-3 battles. Battles where a Summon is really good are usually spaced out further than that, although I can think of a couple areas where you get great battles for Summon use back-to-back. There may not be a need to use them, but that doesn't mean they're never good to use; after all, there's technically no need to use the Crystarium or the upgrading system until you're at the end of chapter 11, but very few people ever actually play that way.