Solving them will make you understand the type and pattern of the frequently-asked questions, thereby increasing your comfort level with the actual board question paper.
Solving multiple papers and checking the answers against the solutions written by experts helps you analyze your strong and weak points.
When you finish one paper a day, and within 3 hours, you get used to a pattern and know how to divide time. When this keeps repeating regularly, accurate and approach the paper with more confidence.
Knowing the marking scheme of the board exam helps in preparing accordingly and students can focus on questions and topics carrying more weightage.
When students work on improving their weaker sections, they perform better with practicing sample papers. This enhances their confidence and they do their best to get good marks.