There are some installations that are more complex and best left alone as installed by the developers installers.
But the simple third party installations will tend to add locations that are unnecessary.
As @Benjamin Drew, I have found it best to take control and use those same two locations. The Steinberg folder for example is completely un-needed. And having multiple folders all over the place seems to hamper performance.
There is a third folder in my installation, "common folders" or whatever for vst3, but it seems it is also optional, helps with organization etc..... But as it stands at this time, beyond Melodyne's integration etc, I have found zero benefit in vst3 and plenty of buggy reasons to decide to not install or use them at this time unless an exception is found.
Currently in my case, I use 64 bit versions, have some 32 for legacy projects and collaboration reasons only. This approach has been working well in multiple DAW's for me. (Full disclosure, Mixcraft is my first choice. There are some very specific functions where another may be used, and some are installed largely for reasons that come up in collaborated projects etc.)
When using Mixcraft 64 bit, and using a plug-in where I have both 32 and 64 installed, Mixcraft loads the 64 bit version as desired. And like I said, 32 bit plugs are only used for old projects or Collabs where the other user has them loaded, or only 32 bit versions are available. Works for me!