In the normal course of creating and modifying workbooks, data structures are frequently allocated with more space than necessary to reduce the time spent growing them. GC attempts to reduce the size of these data structures, potentially saving a significant amount of memory.
Memory can also become fragmented. GC attempts to group related objects closer together which can improve performance of calculations for certain workbooks. As a general rule it is best to call GC once after at least one, and possibly multiple calls to CalculateFull.
The best way to find the optimal use of GC for your workbooks is by benchmarking your real world cases.
Target Platforms: Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2