But, the point of exhaustion is simply that...
You shouldn't be able to "defend yourself better" (defensive) or "attack more quickly" (offensive) if you are exhausted. (As neonovas stated.)
However, if you use a style that simply "drains stamina," and you accidentally drop to 0 stamina, a "default" stance would greatly help the requirement of having to "retype" /s X during the situation that caused you to accidentally drop to 0 stamina in the first place. (Whether that was getting adds, a CC broke, etc.)
Most tanks, including I, try our best to never use the last 5-10% of our stamina bar where we won't be "forced" to drop to /s 1. (Since, with 0 stamina, you can't change to /s 3 <or 12 for me since am a warrior>.)
Thus, simply putting a command to set our default stance would greatly help in this specific case.