The primary reason to use the 64-bit version is its ability to handle larger amounts of memory (RAM).
: Unlike the 32-bit version, which is limited to roughly 2 GB of virtual address space, the 64-bit version can utilize the full range of system RAM, making it ideal for power users of Excel and Access .
The biggest headache with Office 2010 64-bit? Most banks, ERP systems, and Adobe plugins were compiled for 32-bit only. If you need legacy macros or ActiveX controls, stick to the 32-bit version.