Restructures are almost always (maybe always?) good for the player. They take the base salary for the current year and convert it to signing bonus. The signing bonus is paid immediately, but the cap hit is spread across the remaining years of the contract.
So, for example, if a player has a five year contract for $5m per year (5/5/5/5/5 against the cap), and the team restructures the first year, the player still gets the same money, but the cap hit becomes 1/6/6/6/6. There may be some additional rules about minimum salaries, duration of spreading signing bonus, and so on, but that’s the gist of it.
Restructures are basically always good for the player (they get the money now instead of later) and let teams kick the cap hits down the road to later seasons, when the cap will almost certainly be much higher. In fact, often teams don’t even need player permission to restructure because there’s no downside. Eventually the bill comes due, but that’s when extensions come into play...