When would anyone possibly ever use 4 '63 Spring Reverbs, and a harmonizer strung together in practical or live use.
Never, if they're using a POD. The point, again, is that Line 6 chose not to meet the hardware demands of the software, in order to price it at $500. If they had chosen to meet those hardware demands, you could put eight '63 Spring Reverbs in a row. It doesn't matter if no one uses 8 reverbs - This is called quality-control testing. The maker of your car tested it for all kinds of scenarios you'll never use it for, and they do it because they have to. Conversely, Line 6 made a gamble and won on selling the same engineering failure, twice. That's because it was a strong product, even with its flaws.
I can give you two practical examples of why someone would cue up 4 '63 spring reverbs, though:
1. Using a DSP-intensive effect to quantify the available DSP.
2. Any other reason they can come up with. Maybe they're creative, or something.