An outboard bottom bracket gives you fixed chainline, with very little you can do to change it. With recent MTB triple cranksets, that's usually 50mm. That's a bit further out than is ideal for a bike with even 130mm rear spacing. The square taper would give you the freedom to choose different spindle lengths to adjust the chainline. This isn't a major issue, but if you've got nothing else tipping the scales, this could be it.