The phrase "might as well ___" is used when there's an action that's not happening yet, but it's almost happening. For example, if you're eating a dessert and you finish 90% of it, there's not much difference between eating 90% and eating 100%. You say:

I might as well go ahead and finish it.

Or if you have to travel to another city for work, you might decide to spend the weekend there as well and explain your reason like this:

I might as well enjoy myself since I'm there.