Have you ever set the your camera for certain conditions and then used it under different light, only to find out that you forgot to change it back and now your settings turned to be all wrong? Most often this happens with ISO; set it to high in low light conditions and shoot at 1600 or higher next day in broad daylight, getting unusually high level of noise in the sky. Or setting IBIS to off while shooting on a tripod and forgetting to turn it back off when shooting handheld next day. Annoying, and may cause lower quality or even lost images.  

Seeing how many folks do this, I thought I'd describe how I handle this to eliminate or greatly minimize my chance to run into this problem.

If you have your camera in any of the PASM modes, it defaults to the last set of settings when turned off and back on. That's convenient in a situation where you have a prolonged shooting session under the same light. You don't have to set your camera all over again every time you have it on again, as it retains all your configuration from before you turn it off. The flip side of this of course is the problem described at the beginning.

Custom Modes to the rescue.

Instead of using PASM, I put my standard configuration on the C1. This mode is my starting point for the most frequent situations. For me such configuration is Manual mode, ISO 200, f/5.6, 1/250, IBIS S-IS1, WB Auto, single center point focus in S-AF-M, LSF+RAW, and other standard settings for your garden variety landscape shooting. This way, any changes I make during shooting session won't be retained when I turn the camera on next time. Instead it will default to this standard configuration. No chance of shooting next day with ISO 3200 under bright sun. It's also a quick way to reset everything to the starting point if I change too many parameters and want to cancel all the changes without remembering each of them. Just Off and On, and I am back to my standard configuration.

Configuring camera this way, you can have advantage of both approaches without their respective downsides. If you undertake the long session under the same or close lighting conditions, you use any of the PASM modes, set your camera to your liking and presto - off and on, and your configuration is still there. Done with that - switch to your default starting point, C1. Now when you shoot something different today or tomorrow, none of that session settings mangle your files. While I use the rest of custom modes for moving targets or tripod shooting, C1 is always my standard starting point for everyday's conditions on all my cameras.