You can shape Laval nozzles to have peak efficiency at a specific altitude/pressure/velocity. If you are committed to multi-stage rockets - and there are many r

You can shape Laval nozzles to have peak efficiency at a specific altitude/pressure/velocity. If you are committed to multi-stage rockets - and there are many reasons to do this - then you can have a different shaped nozzle for each stage. This can lessen the advantage of an aerospike and make the extra weight and inefficiency more of an issue. For example, the nozzles on the shuttle's solid boosters were optimized for low atmospheric use, but they were discarded relatively quickly. The nozzles on the shuttle's main engines were most efficient out of the atmosphere.