[simon_void]

Garbage Collections destroys any real-time guarantees you might need, since the GC can be triggered at any time. So for some classes of applications a GC is not an option (e.g. in 3D-video games you don't want your rendered frames per second to drop under 60 frames per second).

[packetlost]

Rust doesn't generally have a garbage collector though. This doesn't apply to the general case (ie. unless you go out of your way to add a GC into your runtime)

[pebal]

You can have a pause-free GC, where the collector runs in a separate thread and never pauses the mutator threads.