Are there any use cases that people here have experienced where Valgrind is their first choice?
If I have anything that feels like UB, especially that I can trigger in a unit test, I run it through valgrind first. If the issue can only be triggered by running the whole system and valgrind slows it down too much, there's a good chance that sanitizers will also slow it down too much.
Among the sanitizers the valuable ones are the general undefined behavior ones. Valgrind won't tell you about your integer overflows and whatnot. Like that in b >> a, a turned out to be 32 or greater at run-time.
There are some situations where I find myself using Callgrind, in particular in situations where stack traces are hard to extract using a regular profiler. But overall, it's a tool that I find vastly overused.
Callgrind is a CPU simulator that can output a profile of that simulation. I guess it's semantics whether you want to call that a profiler or not, but my point is that you don't need a simulator+profiler combo when you can just use a profiler on its own.
(There are exceptions where the determinism of Callgrind can be useful, like if you're trying to benchmark a really tiny change and are fine with the bias from the simulation diverging from reality, or if you explicitly care about call count instead of time spent.)
In effectively all latency-sensitive contexts, sampling is worthless. 99.999999% of the time the program is waiting for IO, and then for a handful of microseconds there's a flurry of activity. That activity is the only part I care about and perf will effectively always miss it and never record it to completion.
I need to know the exact chain of events that leads to an object cache miss causing an allocation to occur, or exactly the conditions which led to a slow path branch, or which request handler is consistently forcing buffer resizes, etc.
I never need a profiler to tell me "memory allocation is slow" (which is what perf will give me). I know memory allocation is slow, I need to know why we're allocating memory.