A highly detailed and accurate Bill of Quantities (BOQ) is essential for effective cost control in construction projects for several reasons:

Basis for Pricing: The BOQ provides a comprehensive breakdown of all materials, labor, and other resources required for the project. It serves as the basis for pricing and helps in obtaining accurate cost estimates from suppliers and subcontractors.
Cost Monitoring: With a detailed BOQ, project managers can monitor costs more effectively throughout the construction process. They can compare actual expenditures against the estimated costs for each item, identifying any discrepancies early on and taking corrective actions promptly.
Budget Management: Accurate cost data from the BOQ allows for better budget management. Project stakeholders can allocate funds appropriately, track expenses against the budget, and make informed decisions to avoid cost overruns.
Tender Evaluation: Contractors use the BOQ to prepare their bids for the project. A detailed BOQ ensures that all bidders are pricing based on the same scope of work, enabling fair and accurate comparisons during the tender evaluation process.
Change Management: During the course of a construction project, changes are inevitable. A detailed BOQ provides a clear reference point for assessing the impact of changes on costs. It helps in evaluating variations, issuing change orders, and minimizing the potential for disputes related to cost adjustments.
Risk Mitigation: By having a comprehensive breakdown of quantities and costs upfront, project stakeholders can identify and mitigate potential risks more effectively. They can anticipate cost fluctuations, market changes, and other factors that may impact project expenses.
Contractual Compliance: A detailed and accurate BOQ ensures that all parties involved in the project understand their contractual obligations regarding quantities, rates, and pricing. It helps in resolving disputes and claims by providing a transparent record of agreed-upon terms.

In summary, a highly detailed and accurate BOQ is critical for effective cost control in construction projects as it provides a solid foundation for estimating, monitoring, and managing costs throughout the project lifecycle.