
Fearless is a pretty straightforward card. I honestly don't see any reason not to include in any deck that relies heavely on Spells, which is to say, most decks of investigators.
Most of the Spells assets require that you do a skill test. With one icon to commit, Fearless helps you do just that, and providing you succeed, it heals 1 horror.
Some of those Spells inflict horror damage when you draw a non-numerical chaos token (example: Shrivelling), so you might want to mitigate those downsides a bit.
In any case, that card is always good encounter deck mitigation, as a lot of treacheries throws tests to the investigators, and the game has many ways to inflict horror you might want to heal.
Great great card.