The obvious cases for not using garbage collection are hard realtime, severely limited memory, and wanting to do bit twiddling with pointers. Are there any other, less discussed, good reasons why someone would prefer manual memory management instead of GC?
It IS possible to use garbage collection with hard real time, if you have fully incremental garbage collector with bounded execution time per byte of allocated memory, so, crazily enough, it is NOT necessarily a reason not to use garbage collection :)
One fundamental problem with garbage collection, though, is that it is difficult to estimate and manage the actual size of the working set in memory, because garbage collector can free your memory only delayedly. So, yes, when memory is restricted, garbage collection might not be a good choice.
Another problem with garbage collection is that it sometimes interferes with freeing other resources such as file descriptors, window handles, etc., because, again, the garbage collector might free those resources only delayedly, causing resource starvation.
Garbage collection can also cause cache trashing, because the memory is not necessarily allocated in a local fashion. For example, stack allocated memory is much more cache-friendly than heap-allocated short-lived objects.
Finally, garbage collection of course consumes CPU time :) So if you can code manually memory management you can save the CPU cycles the garbage collector would consume :)