Could/might just as well…
Definition 1 of 1
Pro Tip 1/3Alternative Suggestion
Use when proposing another option that seems just as acceptable or suitable. 
You could just as well take the train if the buses are full.
Pro Tip 2/3Pointless Effort
Expresses that an action has little or no value, so an alternative wouldn't make a difference. 
We might just as well cancel the picnic if it's going to rain all day.
Pro Tip 3/3Mild Criticism
Implies that a current effort is insufficient and something else could be equally ineffective. 
He could just as well have stayed at home with that lack of enthusiasm.