By definition, the whole guitar signal is sent to the bus, as the bus = grouping. If you're taking a split it's called an auxiliary send.
There aren't really any rules of thumb, it's just what sounds good, and what you like.
Saying that, I often tend to put an LA3a style comp on the bus, often not even pulling any dB, just because I like the way it pushes the mids. If it's just double tracked (1 left, 1 right), I sometimes add a small amount of pitch shift in parallel to help widen and thicken the sound.