Planning the save game system for your game is essential. The platform being used, the type of game, and the programming resources all must be taken into consideration.
What kind of save system?
Do what other games that are similar to yours do — and then try to add some improvements if possible. Many shooter games, especially on consoles or hand held devices, have save points — the player does not choose to save the game. As an RPG designer it was always my belief that ALL games should allow save games whenever the player wants but occasionally, usually for issues of difficulty, a save point system makes more sense, from a design point of view. If a player reloading before every big fight will ruin the experience, don’t allow it.
When (in the schedule) to put in a save system
The earlier this system is planned and implemented in the engine the better — it will improve the ability of QA to accurately stress test the game if they are able to plow through it as intended. In addition save games tend to put a giant spotlight on general area load issues.
Also the earlier the save system goes into place the more iteration will be available to make it faster and to shrink the file size.
Autosaves are a type of savegame that saves automatically when the player reaches a certain point. Generally autosaves are a good idea but do consider how you draw attention to them. For example, if you have an option to disable or enable the autosave you must assume that the player will expect every potential situation in which they could die to be saved for them. It being an option suggests that this is the case (i.e., the game designer is going to watch my back for me).
In my opinion it is better not to have an autosave option. Either have autosaves or don’t have them — the player shouldn’t decide this.
Children Are (Often) Evil
If the game is meant to be played by children who cannot read (I’m looking at you, Littlest Pet Shop) require a password before save games can be deleted. The number of times our kids have been reduced to tears because they deleted the save games (and all the little animals they have collected) is beyond counting.
This is actually a side benefit of the Wii Fit’s privacy password system — our kids have deleted their accounts numerous times but we’ve password protected ours, thus saving them from random deletions.