It's a good idea to complete a nice portion of these early on, as players will earn additional experience points to allocate toward unlocking more skills for Faith. (nerdbite.com)
Characters can also gain additional experience points and items and bring them over to their single or multiplayer campaigns. (totallygn.com)
For example if you can continually defeat monsters without much of a break the game awards you with additional experience points once your string of kills ends. (the-bitbeacon.com)