• Decreased performance, as DRM is often hooked deep into event loops and adds non-negligible overhead.
• Decreased privacy, as DRM often requires pinging an external server constantly.
• Decreased security, as DRM is a black-box blob intentionally meant to be difficult to peer in to, and has been the target of attacks such as code execution vulnerabilities before.
• If you own a game but don't have an active internet connection, DRM may prevent you from playing the game.
• If you own a game but have multiple computers, DRM may force you to buy multiple licenses when you're only using one copy at a time (c.f., a physical CD with the game on it).
• Eventually, a DRM company is going to go out of business or stop supporting old versions of their software; if you want to play an old game that had that DRM, you won't be able to even if you own the game.
• &c.

DRM exists to "protect' the software developer, i.e. protect profits by making sure every copy has been paid for and to force people to buy multiple copies in certain cases. DRM never has and never will be for your (the consumer's) benefit.