... of course, to a fair extent, the message here is "Read your contract, and don't sign away things you shouldn't." Non-compete clauses on low level jobs would dry up pretty fast if everyone that saw one in their contract said, "No." Which they, y'know... should be? Don't, obviously, but still.
Though, sadly enough, the methodologies behind sandwich making actually can be a notable trade secret. Order of construction, layout of rooms, particular variations in materials, various corp-standard customer interaction bits... the list kinda' goes on, and they're all things that can substantially impact profit margin over the course of a business's life, especially for chains. There is a fair amount of bullshit going on, but it's far from entirely so, and a competing business being able to cheerfully acquire the fruits of the (often disturbingly substantial) research that goes in to refining that sort of thing just because they managed to snatch up a previous employee...
... it's like, personally, I'm kinda' okay with corporate espionage of pretty much all (non-violent) sorts -- whatever spreads efficient and/or effective methodology the furthest is more or less what I want to see, and if some big wigs lose some portion of their profit margin because of it, I don't entirely care. Being marginally less rich isn't exactly a hardship. But I can definitely understand why businesses would be protective of stuff they've often sunk thousands behind the scenes into developing. Making several hundred sandwiches per day is not just throwing some stuff between two slices of bread and calling it an afternoon. If your company has figured something out that shaves a second or a half-penny or something off each sandwich, you've got a pretty damned significant competitive edge that you actually do kinda' want to hold on to. And never mind more obviously complicated industries.
Though to be clear, I wouldn't exactly complain if there was regulation implemented to curtail particularly predatory employment contracts. Just noting that it's pretty understandable why a company -- particularly a larger one, that has a hefty amount of time and/or research sunk into its methodologies -- would want to keep people it has trained out of similar fields. They've got a lot riding on what your average outsider might consider to be inconsequential things. And that they've reached the point where they apparently see the need to contractually ensure their former employees immediately spill every competitive edge they have to competing businesses is telling in its own way...
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Though yeah, @ Helg: It's actually pretty rare from my understanding that small wage differentials are enough to cause immediate ship-jump like what you're describing. I can almost guarantee you there was either a significant wage difference or something else going on -- extra benefits, different work environment, etc. Little benefits are usually not enough to cause people to take on the risks that are involved with that kind of rapid job change.
Mind you, SG's points are also spot on.