I avoid closed-source tools as much as possible. But sometimes they happen to be the most performant choice. I've seen the claim that the Dyalog APL is the fastest, for example. Commercial compilers from chip manufacturers (Intel, e.g.) are popular for numerical applications, as the free alternatives, excellent as they are, simply can not make the detailed optimizations that the targeted compilers can. The chip makers invest in developing these compilers because they make their systems look fast on benchmarks.
Commercial compilers from chip manufacturers are common in embedded world - from Keil and IAR for ARM (you can use GCC but the code quality wouldn't be that good) to almost everything proprietary down the road to FPGA and ASIC.
> (you can use GCC but the code quality wouldn't be that good)
Maybe.. on the other hand you can actually use the full program space available, and gdb. (Last time I used Keil was 2011, I quickly moved to a GCC toolchain rather than pay for a license. They're really not selling me on their tool when they arbitrarily restrict my max program size such that I can't actually evaluate it properly.)
