I find the keyboard best for expanding/collapsing multiple folders. If you select the ones you want to expand first, then simply use the left or right arrow keys to collapse/expand, respectively. With the addition of the Option key modifier, this action takes place on all subgroups within the selection as well.
In addition, for absolute expansion and contraction, see View ▸ Outline ▸ Expand All and ... ▸ Collapse All, along with their associated shortcuts.
.:. Ioa Petra'ka “Whole sight, or all the rest is desolation.” —John Fowles