Hmm, ok. But how is that different from situations where tracing GC is useful? (And even languages with a tracing GC often offer weak pointers. Eg Haskell and Java do. Python does as well, but Python has both reference counting and tracing garbage collection.)

Apart from performance (latency vs throughput) considerations, the only difference between RC and GC for your algorithms and datastructure design is whether you allow circles in your datastructures.