no worries, either way will work fine. I'd say it's generally safer to install without it, as it's easier to automount. I've had problems in the past when my computer expected the drive to be there on bootup, and I'd forgotten to turn the power on, so it failed to boot. There are ways to make it work if you want, but if you don't, just stay away from it during install, reboot then plug it in, it should be autodetected, and you should copy your files no problemo.
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