Traveling is a wonderful thing. Traveling with devices that aren't charged or aren't able to be charged is not a wonderful thing. Luckily, there are travel power strips that will let you and your companions charge devices to your heart's content.
What's great about these power strips is they also come with lengthy cords that help ensure you don't have to sit so close to a wall or outlet in an inconvenient place. Many of these power strips also have smart outlets that can auto-detect and deliver optimal current output for your connected devices. This saves time and ensures your devices are ready to go as quickly as they can be. They are also very safe and provide protection from short-circuits and overheating.
Given how surges can happen at any time, you don't need to worry about when to use a protector; just use it all the time. The real question is what you should plug into a surge protector.
You don't need a surge protector for your desk lamp or your standing fan, but you do want a surge protector for expensive devices that have intricate microprocessors, like computers, televisions, stereo systems, and media centers. In short, anything electronic and expensive benefits from a surge protector.
Think of it this way: if there was an electrical surge that destroyed all of the devices connected to your outlets, which lost devices would pain you the most? Plug those into a surge protector. It's better to be safe than sorry.
It would never hurt to have a surge protector in your carry on. This means that you have unlimited charging power. If you are stuck at the airport and need to charge more than one device, you can if you have a surge protector. Most surge protectors have outlets as well as USB ports now, too.