The primary benefit of 1-on-1 lessons is individualized attention. The average class size in most high school and university education is between 15 and 25 students. Teachers follow their lesson planning and differentiate as best they can for the students who need extra attention or who benefit from an accelerated course, but there is a limit to what they can do with the time they have. With private tutoring, areas of difficulty can be identified quickly and instruction can be targeted to help the student excel far more efficiently than in a normal classroom.
Students also benefit from being able to work at their own pace. There's no one else to shout out answers before you have a chance to even understand the question, no more pressure to keep up or fall behind, no more anxiety or embarrassment when you struggle. The tutoring session exists solely for your benefit.
The final benefits of tutoring are accountability and motivation. When working with a live tutor, students have to show up and participate in the lesson or else it doesn't take place. Whether you're scheduling tutoring for yourself or your child, when you make the effort to reach out to someone, talk to them about your needs, and ask them to set aside time to help, you create a social pressure to come to class and "get your money's worth."