Earlier quoted context omitted.
It should be whatever is highest between your current salary and the new job offer.
That sounds abusable. You get some company (possibly owned by a friend of yours) to offer you a massive salary, then your original company has to pay that massive salary for 3 months or whatever. Then as soon as you start at the new company, they fire you.
Noncompetes are terrible, and you should be prepared to pay out of your nose if you want to keep an employee off the market.
As long as you're not forced to pay that money, it's all good. It just means that the employee can actually switch jobs immediately (for a better pay or not) unless you're willing to pay them however much they're willing to stay out of the market for.
Say I make $100k today. I get an offer at a place I really like, for $150k. I'd really like to go there, but they're also a competitor. I offer to stay home for $200k, and if you don't want to pay that much, then I go to work for $150k.