I think you are referring to deallocating an object graph. Under GC, the cost of deallocating an object graph depends on global state, such as how many unrelate

I think you are referring to deallocating an object graph. Under GC, the cost of deallocating an object graph depends on global state, such as how many unrelated objects are allocated. But in an RC scheme, the cost of deallocating an object graph depends only on that graph itself. This makes RC easier to reason about. The "unexpectedly long" cases can be isolated and optimized separately. Consider a soft real-time environment like a game. Under RC, the time required to render a single frame depends only on the work done in that frame. Get it to 16 ms and you're done. But under GC, deallocation work can accumulate. A frame that would otherwise render in 16 ms may take much longer, due to the laziness of previous frames. That makes it harder to optimize, and indeed you'll often see advice like "frames must do zero GC allocations." Yikes! Things may be different in hard real-time systems, which I know use specialized allocation schemes optimized for worst-case latency instead of bandwidth.