It is not just a heuristic if you have hard upper bounds on the things that matter - in that case, it is static analysis. A missile has a limited, and well-defined, fuel supply.
In the case of memory management, it is not enough to just free it after use; you need to ensure that you have sufficient contiguous memory for each allocation. If you decide to go with a memory-compaction scheme, you have to be sure it never introduces excessive latency. It seems quite possible that to guarantee a reallocation scheme always works, you have to do more analysis than you would for a no-reallocation scheme with more memory available.
