For one - profitability. Dead money is typically some money that was paid in past seasons via signing bonuses and restructure bonuses. So by having it on this years salary cap - spending is kept down, but we still are "spending" to the cap threshold. If you're not going to be good... it's helpful to the owners that the bottom line looks ok.
Two - Assets. We got a lot of picks in trades and were able to do what Whaley never could - get a QB. We were going to cut tyrod and got the 65th pick for him - and didn't have to eat any base salary. Sammy was a pending UFA, who we were unlikely to negotiate with at the time (his value was really up in the air and dependent on his performance in 2017) - and we got a 2nd round pick for him.
Three - Flexibility. When you don't have cap room, you tend to not negotiate extensions for players. You then lose players in free agency. We were unable to keep hogan and gillislee because we were cap-strapped. We had to lowball their tenders, and lost them on offer sheets. Gilmore/Woods are the same kind of thing - couldn't extend them prior to losing them.
Last offseason we had to bring in help at safety (google our 2016 safeties) - and that was about the only position where we brought in a top tier free agent. This season we had to address rush defense, so they went with Star (don't love the signing).