Others gave great replies.
If you do simple and straightforward actions, then it performance shouldn’t really matter, but it’s better to profile if you notice any issues rather than worrying about performance before you’ve even made anything.
It’s worth keeping in mind some Widget functions are configured to be cosmetic only, which means they might run multiple times in the background as the user interacts with the UI. Ideally you don’t want to add anything gameplay-specific or expensive, but that’s also something easier dealt with after it becomes an issue.