Do I need to save my game manually?

In Grand Theft Auto V on PS3 or Xbox, do I ever need to save my game manually (by sleeping in a bed or using my cell phone) or can I rely completely on the auto save feature?

A related detail, inspired by Nolonar's answer below is: If I do save my game manually, using quicksave or sleeping in a bed) should I save it in the same slot as the autosave, or a different slot? Is there any way to prevent the "Are you sure you want to overwrite?!" message that comes up at the start of each play session?

(In both cases, assuming I never want to "rewind time", i.e. I only ever want to load my latest save.)

Solution 1:

The auto save feature is pretty neat, as it'll save after every completed mission, mission replay, random encounter, activity, in short: anything of relevance.
The auto save feature won't save after you improve a skill, however, and if you're in flight school or in the shooting range, you'll have to leave those before the auto save feature does its job.

However, the quicksave feature (accessible from the cellphone) is pretty neat too. Try it out, and you'll never want to go back to your safehouse to save, never. Well, maybe you'll occasionally want to return to change clothes, watch TV, fetch whatever vehicle is in your safehouse garage, or to time travel 6 ingame hours into the future.
The beauty about the quicksave feature, is that it'll save your current position, the vehicle you're currently driving (but not its damage, which is kinda nice) and is just perfect to abuse the stock market. Just quicksave in front of the assassination missions, start the mission, jolt down the stock you'll want to invest in, load the previous quicksave, then invest in those stocks as everyone (as you won't be able to switch while on assassination mission).

Basically, auto save does a good job, but quicksave does an awesome one. Use it well and do it often.

Solution 2:

I've found that the auto save seems to work really well in the game, however before I am done playing for the day I always go and do a manual save. You can access this through your phone (up on d-pad) and then select quick save.