oreocookie
The reason is so that you can't just set it to something and forget about it and then use it with a different mix than it's set for. If you have to set the mix at least every time you turn it on, there's no possibility that you'll forget to change the mix if you use something different from what you normally use because setting the mix will be part of your pre-dive routine along with setting up gear.
Yea thats what I figured. I just assumed since checking your computers battery and making sure it works pre dive is just part of the routine that extra safty net isnt' needed.
By default it's turned off, if I remember correctly. I know I have it set for off at least.