How does a butt joint with an insert improve welding strength?

A butt joint with an insert improves welding strength primarily by addressing the integrity of high-strength steel. When high-strength steel is used in construction, such as in vehicle frames or structural components, it can lose some of its inherent strength at the joint due to the heat generated during welding. Adding an insert helps to reinforce the area, compensating for any weakness and enhancing the overall structural integrity of the weld. This method ensures that the joint can handle the stresses and strains it will encounter in service, maintaining the strength characteristics of the materials involved.

While eliminating the need for additional parts or creating a more complex joint structure might have benefits in some contexts, they do not directly enhance the strength of the weld as effectively as reinforcing high-strength steel does. Simplifying the welding process could also be advantageous, but it is not the primary function or benefit of incorporating an insert into a butt joint. The focus on restoring and maximizing strength is what makes option B the correct answer.