Let's try this again.
Say Vince wants $8 million a year.
Previously that might have been difficult.
But in an uncapped year, you can do this:
$12 million in the first year, $6 million in the second, third and fourth.
That literally means that because of the uncapped year, you managed to keep Vince within your salary cap budget of $6 million (assuming the Patriots had his value pegged at $6).
The uncapped year allows the Patriots to meet their objectives and it doesn't fall afoul of the uncapped year's 50% rule.
UPDATE: all it really means is that Kraft shells out more money up front. I am of the opinion that the Patriots should be aggressive with their own FAs and any FA they deem fits the Patriots' style. You can project a future salary cap number (say, $160 million) and then make sure that in future years all contracts stay below it, so that you don't get in trouble, but that means you can still take advantage of an uncapped year by frontloading all contracts.
Pretend that no one was signed onto the Patriots for next year. You could sign players for a $320 million payroll next year, and then the year afterward you could be below $160 million, and you'd never get in trouble with going over the cap. (This is a hypothetical, I'm not interested in discussing whether it would be prudent to spend $320 million, its impact on players, blah blah).