There are no rules, but I think always tracking in stereo is generally a good idea. I would take it a bit further and say always track in M/S, stereo and with room mics. It gives you more options at mixing stage which is very important. Overdubbing + M/S + Stereo + Room mics can sound very full and natural. It allows you to use the room more efficiently, hence you don't need to rely on reverbs as much and you end up with a better final mix in the mastering stage. Try, free yourself to new creative possibilities. Stop doing everything "right". Play with power and possibilities and have fun while doing it! I think Bob would agree.
Don't waste possibilities due to some rules on the Web. Imagine how much you can color sound by using several mics processed differently. Always using only one or two mics for everything is simply stupid.
Tracking is where interesting stuff is born. Make sure you track such that you can easily discover new things about your mix to get ideas of how to mix it in the most interesting way. This means for instance track many guitar amps, or even better, many guitarists using many amps in many rooms with many mics ha-ha...! You can always find new better options. What options can YOU find?! Good is not good enough, go for something unbelievable! Only natural is a trap, don't fall into it!
<B>SO MUCH OF A GOOD SOUNDING MIX IS IN THE DECISION MAKING PROCESS</B>
You know, at worst you waste an extra mix channel, at best you made the mix rock! Why limit yourself to only a few options when you can make a mix rock by giving yourself a few additional options. Give yourself plenty of options, then choose wisely.
One more thing: HAAAAAVEEEEEE FFFFUUUUUUNNNNNN!!!!!!!!