When you deploy, you have a specific version of your application, the bugs and features, the flows, the pages, the domain model etc.
When you restore, you get a specific backup for your database, your data, tables, objects, associations and optionally your filedocuments.
It's more or less software vs. data. Most of the time you'll deploy new versions of your application keeping the same database and files. Mendix will implement domain model changes in the database. When you want your data back from a specific point in time, you can restore your data and files. Maybe also deploy an earlier version of your application, that depends.