TMC might know more about how likely to be earned (LTBE) and non-likely to be earned (NLTBE) incentives work now in the new CBA. Tricks using those two things were used a lot back when salary cap room couldn't be "carried over" into the next year (like it does now).
The old rules on incentives were like this:
An "incentive" in a contract is categorized as LTBE or NLTBE. How that is determined is a bit of a mystery but mostly if a player reached that incentive LAST YEAR, then it is considered likely to be earned. Brett Keisel had 564 snaps, 4 sacks, 20 tackles and 9 assists and 1 forced fumble in 2013.
If you put an "incentive" of like 500 snaps or 2 sacks or 20 tackles into Keisel's contract (things he might agree to), then those things would be classified LTBE.
LTBE incentives count immediately on the salary cap. It's like they are considered base salary for the purposes of salary cap accounting. If you make an incentive that in UNLIKELY to be earned (like let's say 5 sacks for Keisel), then if would not count on this year's salary cap.
At the end of the season when all these incentives are either gained or not gained by the players, you adjust what happened on your salary cap books in the next season (so if you've been carrying a LTBE incentive on your books all year and the player didn't get it, you gain a CREDIT on next year's salary cap). If you haven't been carrying an ULTBE incentive and that player gets the bonus, then you add that money to your next year's salary cap accounting (thus you get less cap room for next year).
That's how incentives work (or they did in the old CBA)