In a string and pulley problem, will friction increase or decrease the tension.can you please explain if you can?

Adding friction to a pulley problem, regardless of if a mass in on an incline or not, will almost always increase the tension in an atwood machine- type pulley problem. This is because friction will always oppose motion, so there will be more forces working against the force of tension. Therefore, to make the mass start moving, the force of tension will have to be greater than it would be if the system was frictionless.