That can't cut it any longer. Many of the problems don't occur on one machine. Adding a profiler to your code won't reveal the real bottleneck, which could be caused by some weird interconnection or a sluggish database. Modern tools track the network calls for the network of software as well as the performance of individual modules. This is the only way to understand what is going right and going wrong.
This is just one important way of how the model of programming is morphing from a single machine to a network of connected tools that may or may not play well together.
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