And btw we have a slew of LPs using this technique in production in exactly the same way Christine describes, letting users view different product groups on the same LP by clicking different email links.
We use a Velocity script to check if they are already hard-segmented in the database; if not, they can soft-segment themselves, which we then commit to the database afterward.
I just tried setting this solution up and might've stumbled across the snippets not being necessary - just the segmentation?
I'm using this in a guided landing page, that didn't yet have any snippet section added in the template... Before I started adding the snippet piece into my template, I tested something: with a segmented html text area, the variable passed in the url perfectly fine! I checked in an incognito browser, and I'm not catching any issues. I'd thought the snippet was a key component for it to work... but seems it works this way as well.