Vantaggi
The pay is good(but see below) . I've worked on commercial accounts rather than the typical Government contracting role that Leidos (formerly SAIC) is typically known for. I have worked for government contracts on government accounts in the past so I can see how much the company runs like a government contractor. Commercial businesses work a bit differently, though, and so sometimes Leidos is a bit slow to move compared to the accounts they support. Mostly though, they've stayed in the background which is fine by me. Much of my career satisfaction and growth has really been driven by the customers we support and my immediate management rather than by Leidos further above.
Svantaggi
The erosion of benefits as others have mentioned is really a pay cut. Various changes as well as minimal performance increases despite being rated highly and working on profitable contracts. Leidos has taken a beating on some other contracts and been fined and those costs have been passed throughout the particular organization I work for. If you lose coverage on a contract you will lose employment. Leidos' business model doesn't support the notion of a "bench".