depends if you want the same EQ applied to all 4 guitars. If you're quad-tracking with a couple different amps they'll probably require differing EQ setups. If you used the same amp for all 4 you still may want to EQ the 2 sides a bit different to give a wider stereo image. You can save the bus / group global EQ for more musical, overall changes like "damn, all my gats is dull, needz moar edgez"