The restore dialogue in SSMS has a GUI front end and works for one database at a time. sp_RestoreScriptGenie can build a restore script for all databases in an instance (handy if you have 50 or 60) and can be scheduled as a SQL agent job to, for example, automate development environment refreshes, reinstate log shipping, mirroring, alwayson availability groups and so on.

The functionality available in the ssms restore dialogue and sp_RestoreScriptGenie and very similar (I hope to make it identical by adding file group and page restores) but the circumstances you might use each in are different.

Thanks for the question and best wishes

Paul