A zoom climb is a useful (perhaps only) way to get to the top corners of the flight envelope for engine & airframe handling testing, certainly for military aircraft. An example.... Up there surge margins are er... marginal and finding out what happens is important. A graceful flame-out is a good result; a locked-in surge, where things get rather warmer than they should, is not such good news and behaviour and recovery actions need documenting from flight test so the right guidance goes into the AFM or system behaviour is modified to prevent service pliots and their aircraft being exposed to such unnecessary excitement.
A zoom can also be used to get into position to dive onto flutter test points if the performance gurus' modelling shows that's the best way to get there.