By enhancing snippets in your account and then saving them, you're improving the overall quality of messaging in your account.
There are two ways to save snippets, either as new, or as an update to the existing snippet (overwriting). It's important to understand the implications for both.
When to "Save as New"
You've modified the text of an existing snippet. You've also likely added new Personas, Trigger logic, or Logic sets to an existing snippet of text. You want to save the changes you've made, but you still want to have the previous version available in your account.
You want a variety of messaging options for the same situation a campaign may be suggested for. So when you hit the refresh wheel, the Autobound user has a different voice/positioning.
When to "Overwrite"
You're enhancing an existing snippet and want to overwrite the previous version with your new changes. The previous version will not be shown in future suggestions, given it's now been overwritten.
Often times, you'll just be enhancing the messaging in a snippet when you choose to overwrite, rather than changing the Persona, Trigger, or any other 1st party logic (ie. Activity not traction, user colleague opportunity traction, or any custom CRM logic, etc.)