Making the shift to 64 bits
We are currently working on embracing the future and are transforming Capture to a 64-bit application in time for the upcoming version 22 release. You may argue that it's not the future as much as the present already, but with half our users running Capture on Windows we had to wait until the statistics worked in our favour as we don't have the resources to maintain both 32-bit and 64-bit distributions. While the first 64-bit version of Windows came some 15 years ago with Windows XP, adaptation has been slow.
Benefits of 64-bit applications
Generally speaking, the largest advantage for 64-bit applications is the ability to use more memory. A 32-bit application is normally limited to 2 GB on Windows and 4 GB on Mac OS X. If you are working on large project files and/or importing complex models this may be a real problem. Keep in mind that while you might not have Capture files the size of several GB, there is also memory overhead during project open/save, when importing 3D models and for maintaining the undo buffer, especially if you work for a long period of time. We have seen a few users with particularly large project files running into such problems recently. 64-bit applications don't suffer from such memory limitations and can use all memory available to them, opening a whole world of possibilities.
Also, 32-bit applications are already in a sense second class citizens on both Mac OS X and Windows. Windows runs 32-bit applications differently from 64-bit applications and keeps their settings separately. On Mac OS X the original 32-bit "Carbon" framework has been deprecated for a while and new applications are expected to use the "Cocoa" framework, a requirement for applications that want to use new modern features such as Retina resolution.
Consequences for Capture
Ironically, considering the hard work that is going into the 64-bit shift, we don't expect many users to see any difference. Capture may install faster on Windows, look a bit more modern on Mac OS X and work better with large project files, but the only new feature that depends on the shift is the ability to read SketchUp files from 2015 or 2016 on Mac OS X (as the toolkit we use from them to read the files are only available in 64-bit versions since 2015).
What do I need to do?
If you're an Apple user - nothing! Mac OS X has a much more transparent approach to 32-bit and 64-bit applications than Windows and does not maintain separate OS versions for the two architectures. In fact there was a period during which most apps for Mac OS X internally had both 32-bit and 64-varieties so that the OS could choose which to run, but nowadays most Mac OS X apps are only distributed as 64-bit.
If you're a Windows users and you are still running 32-bit Windows, you will not be able to run Capture version 22. If you are about to upgrade to a newer version of Windows, make sure that you upgrade to the 64-bit flavour. If you are not upgrading, the only option remaining is to reinstall Windows, where fortunately Windows licensing allows you to reinstall Windows from 32-bit to 64-bit without problems.