Once upon a time, I ported a turn-based strategy / tactical combat game to the web. The average play time for the game is quite long (many hours), so saving games is an important feature.

PC/Console games have two ways to do "game saves":

1. Save on the machine, keyed to the user thanks to the operating system's file system and
2. Save on the cloud, keyed to the user by some identity provider.

1) is easy to implement (writing and reading a file to disk). 2) is much harder to implement, costs money to run, and requires the gaming machine to have network connectivity.