Comprehensive and Detailed Explanation:
The primary purpose of IT capacity management is to ensure that IT infrastructure can meet current and future performance requirements in a cost-effective manner.
Option A is correct because it directly relates to capacity management goals.
Option B (rapid deployment) relates more to change management.
Option C (security concerns) is outside the scope of capacity management.
Option D (reducing cost/time) may be a secondary benefit but not the primary objective.
# ISACA Reference: CISA Review Manual 27th Edition, Domain 2, section on capacity management and IT service performance.