The 32 bit versions of Windows desktop OSes are limited to 4 GB at most. Home Premium X64 is limited to 16 GB. The 64 bit Professional, Enterprise, and Ultimate all support 192 GB.
32 bit application software uses up to 2 GB of RAM (3 GB for large memory aware applications). More than 4GB of RAM can be useful if you wish to have multiple 32 bit applications running at the same time. 64 bit applications are useful for tasks that must access lots of memory (finite element analysis, video processing, etc.).
As RAM is relatively cheap at the moment, even if you waste it, you won't be wasting much money.
32 bit application software uses up to 2 GB of RAM (3 GB for large memory aware applications). More than 4GB of RAM can be useful if you wish to have multiple 32 bit applications running at the same time. 64 bit applications are useful for tasks that must access lots of memory (finite element analysis, video processing, etc.).
As RAM is relatively cheap at the moment, even if you waste it, you won't be wasting much money.