I'm actually more thinking about the client sitting on the front-end like a single page app. Network instability could cause the response to not reach the front-end after a successful insert. This wouldn't be extremely common but would definitely be a problem for you as the database admin if you have above a certain number of users. I've seen this issue on live production systems and the root cause of duplicate records can be baffling because of how infrequently it may happen. Tends to cause issues that are hard to debug.