What's the deal with Influence Gain in Dungeon Siege 3?

Solution 1:

Gaining influence with allies will go towards earning deeds with each: you receive a deed for earning 25%, 50%, and 75% influence with a specific ally.

At each of these milestones, you gain a number of points in a specific attribute associated with an ally:

• Lucas: Stamina
• Anjali: Attack
• Katarina: Agility
• Reinhart: Will

• 25% influence: 2 points
• 50% influence: 3 points
• 75% influence: 5 points

These gains are cumulative, so you can gain a maximum of 10 points in an attribute this way.

Solution 2:

I've began playing it this week-end. So I did not benefit influence for the moment, but from my experiences reputation systems are used to unlock special parts of scenarios. Maybe you will have gain on a justice trial since they will testify for you. Maybe they will ask you for a special quest because they trust you, or maybe they will give your their father magic ring... who knows.