Consider Costs and Benefits of Coalescing or Rebuilding Indexes
Improper sizing or increased growth can produce index fragmentation. To eliminate or reduce fragmentation, you can rebuild or coalesce the index.
But before you perform either task weigh the costs and benefits of each option and choose the one that works best for your situation.
Table 5-6 is a comparison of the costs and benefits associated with rebuilding and coalescing indexes
Table 5-6 Costs and Benefits of Coalescing or Rebuilding Indexes