Go is certainly a fine language. One common instance where I would prefer C++, though, is when you are writing libraries for others to use. A language that runs on a VM can not easily be used as a library inside a language that uses another VM. You cannot easily write a library for Python in Go or vice versa. If you use a VM-less language like C or C++, your work can be used (through various wrappers, like SWIG or that Apache thing) by everyone.