The things that impact the most are locking/blocking, data duplication (ghosting due to race conditions), and poor performance. The best advice is RTFM the documentation for your database; yes, it is a lot to digest that is why DBAs exist. Most of these foot guns are due to poor architecture. You have to imagine multiple users/processes are literally trying to write to the same record at the same time; when you realize this, a single table with simple key-values is completely inadequate.