Meaning: If you "might as well do something" or "may as well do something", it means there are no reasons not to do it (also when one makes a suggestion that one is not entirely enthusiastic about)
We might as well finish this work tonight. It will only take another half an hour
I'm closer to the Jersey Shore than Long Beach, so I might as well go there instead
This means "There is no reason when one makes a suggestion that one is not entirely enthusiastic about, not to finish this work, as we have nearly finished it already"
We often use MIGHT AS WELL or MAY AS WELL as a short answer.
Shall we finish this work tonight? It will only take another half an hour.
Yes, might as well!
You can see an explanation at minute 6:00 of this video 5 Most useful English expressions