bastion
I've so far found two mementos, a Crystal Barrette and a Ragged Hood. Are these items used for any gameplay purpose, or like the statues, are they just used for narrative flavor?
Should I worry about going out of my way to explore and find them? Not that I don't explore obsessively anyway, but still, my collector's impulse compels me to make sure I'm not missing anything I may need later.
As Mana mentioned, you'll get access to the Smoking Pipe at some point, which allows you to combat waves of enemies in return for fragments. You'll also eventually gain access to the Bedroll and Stockpot, which function in the same way, but offer variation on the narration and enemy types.
More specifically, the Smoking Pipe pits you against enemies from the Old World, the Bedroll pits you against Ura warriors, and the Stockpot pits you against beasts from the Wild. They all offer about the same reward as far as fragments are concerned, and without any bonuses to fragment collection you can expect to get approximately 750 fragments per run.
To increase this amount, consider enabling one or more idols in the Shrine, if you have one. Not only does this give a percentage bonus for fragments collected, completing these dungeons with at least one idol enabled completes a vigil at the Memorial, which will grant you an additional one-time lump bonus.
The only effect you get is extra narration; there's no loot. You're not judged better for not knocking apart the stone/ash statues, either. In fact, the game encourages you to knock them down: there are a few plot points where you have to hit one of the figures to continue, and others where the narration builds on the story of the level when you do knock them down.
Best Answer
Most of the momentos, when shown to The Stranger or other characters, will trigger some specific dialogue revealing more about the backstory of the game. Some of them, however, create monster pets that you can interact with at the Bastion. These monster pets are useful much later on in the game, when...
Other than these, I believe the only other noteworthy momento is the
Ceramic Pot, which allows you to access one of the special fragment-farming dungeons (Who Knows Where).As Shaun notes, you also get a vigil at the Memorial for collecting all 15 momentos, worth 1500 fragments. You don't really need to worry about having to look around for them, as all of them are usually in plain view or down a short sidepath not very far from the main road. If you do miss them, you can buy them later at the Lost & Found.