The ability to influence the minds of others is not something to take lightly. Misuse of the ability, colloquially known as a "mind trick", is a sure step on the path to the dark side. A powerful Force user can manipulate the minds of others to the point where he can convince them to believe things that are untrue, or calm an angry crowd. Conversely, he can rile the crowd into a murderous frenzy, or frighten a single soul into gibbering madness. This is where the danger of Influence lies.
However, Influence is not inherently evil. Many Force users have used Influence to protect the helpless or to deal with a threat in a way that avoids violence. It is much better to convince a guard to return to his post than to have to kill him.
Influence's most basic and arguably crudest ability allows the user to inflict strain on a living target, stressing his mind until he passes out. However, upgrades allow the Force user who specializes in Influence to perform much more subtle and impressive feats.