Depending on how your environments are set up you could do this, but I wouldn't advise it.
Consider the scenario where you have the Staging and Live site publishing from the same CM. In this case all TCMs would be the same, meaning that many of the entries for Stage and Live would likely overwrite each other. If you are storing content in your database publishing to Stage would likely update that content in Live at the same time, defeating the purpose of having two environments.
If you have your Stage and Live environments separated in the CM the TCMs would be different, but the same item IDs would still be used since Tridion just assigns them in order. This means that some references in Stage and Live could end up conflicting, with completely different items in Stage and Live sharing TCMs and overwriting each other in the CM. This would cause a lot of confusion and could also lead to content being published to Live when it's published to Stage, causing risk to your Live environment.
Bottom line is, this is likely going to be more of a headache than just setting up separate databases.