Input nodes can be marked as optional so an end user is able to skip it and not provide an input. To make an input optional, enable the Optional input toggle in the settings at the bottom of the Input node.
This can be useful if you want to add text fields for additional information or comments that a user may not always want to provide. A File Upload can be also be marked as optional, so a user can upload documents only if they need to do so.
When you make an input optional, by default a hint OPTIONAL will display to end users. You can disable this hint in the module configurations.