This effectively reduces the per game fine of salary loss for Gregory's suspension this year. By converting $310,000 of Gregory's $955,217 salary to a restructure bonus, this reduces his "salary" to $645,217. That means his per game loss for each week he is suspended is $37,954 instead of $56,189. It also allows the Cowboys to pay him something this year so he can support his family just in case he remains suspended the full year.
The benefit to the Cowboys is that if he does come back, they don't have to give him a restricted free agent tender next year, which would be $2,144,000. Instead, he gets only $735,000 - saving the Cowboys $1,409,000 next year if the want to keep him. Also, they didn't actually give Randy any extra money that wasn't already budgeted for this year, and finally, the bonus is they created $155K in additional CAP space in 2019.
This means that they don't have to add Randy Gregory to the long list of other young players they want to extend next season, which right now includes Zeke Elliott, Dak Prescott, Amari Cooper, Maliek Collins, La'el Collins, Byron Jones, Anthony Brown, Demarcus Lawrence, Jaylon Smith, and possibly Jason Witten. Not to mention the possibility of getting a new head coach, and coaching staff.