32/64 bit application32 bit processor only can run 32 bit operating system, while 64 processor can run 32 or 64 bit operating system.
The other reason is maximum memory can be recognized and utilized by the system. When using 32 bit processor it's maximum memory is 4GB regardless of what Windows Edition you are using. While in Processor 64 bit can up to 192GB in Windows 7 depend on what windows edition you are using.
In Windows 10 you can add up to 2TB RAM (memory).
Windows 7 64 bit and its maximum memory:Windows Starter Edition: 8GB
Home Basic Edition: 8GB
Home Premium Edition: 16GB
Professional Edition: 192GB
Enterprise Edition: 192GB
Ultimate Edition: 192GB
Windows 10 64 bit and its maximum memory:Windows 10 Enterprise Edition 2TB
Windows 10 Education Edition 2TB
Windows 10 Pro Edition 2TB
Windows 10 Home Edition 128GB
If you are using high intensive memory usage like database applications and video intensive application then the more memory you have, the better your system running.