A lot of people tend to have at least one runtime folder outside of the main Poser installation.

However, I would recommend against putting a runtime in My Documents, as the file path will be much longer than if it's on an external drive or it's own hard drive, and I've run into problems where pz3s had paths truncated as a result, forcing me to tell Poser where the item it was looking for was every time I opened the file.

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If you're joking that's just cruel, but if you're being sarcastic, that's even worse.