>>taubek+(OP)
I once sent out a proposal on the FreeBSD lists to merge /sbin with /bin, and /usr/sbin with /usr/bin. People were concerned that this would slow down the system, due to PATH lookups taking longer. Even when I demonstrated the opposite was true (it being faster due to fewer directories needing to be scanned), I wasn't able to get consensus. What a shame.
>>mekste+fv
Calls like execvp() do little more than splitting PATH on ':', followed by repeatedly invoking execve() on ${dir}/${filename}. The fewer elements you have in PATH, the fewer execve() calls need to be performed in the worst case.
>>cridde+C71
It's probably not exactly going to be hot, but even failing execve is inherently semi-expensive since it needs to be a syscall and incurs context switches.
It's just outweighed a couple orders of magnitude by all the overhead that comes with a successfully launching another executable unless you have, like, a thousand junk paths in your PATH.