Lancer Tactics uses a different activation logic that is very similar in almost all cases. There is no Skirmish or Barrage, instead you have two action points. Some things cost 1, some things cost 2. The equivalent of a barrage is firing two weapons/mounts that cost 1 action point. The primary difference this causes is that you can move in-between firing two different weapon mounts now, unlike in the base game with Barrage. You are not missing any functionality by not Barraging--you're instead gaining a slight positional advantage over the base game which you can choose not to make use of.
The other edge case that isn't covered as I understand it is that intentionally choosing to fire *only* the Aux weapon on a mount with both an Aux and a Main does not give you Bonus Damage from the Aux (if it even has bonus damage)--instead it is treated as a normal activation of the whole mount and you can simply choose not to fire the Main. I'm sure there are very niche tactics where this would make a difference but for the vast majority of builds and players this will have no impact.
If you go to the pinned FAQ post there are a few other changes from the base game mechanics you might be interested in.