The problem: You like to keep your devices charged when traveling but carrying the A/C adapter is a nuisance given it’s size. It’s just so much easier to carry just the cable. But what if those public charging stations have been compromised and someone is using it to steal data? Seems unlikely, right? But ATM skimmers are everywhere so it’s likely only a matter of time. You rely on the ‘Trust this device?’ prompt that iOS and Android give you, but it is not impossible that hackers could compromise the device and prevent the popup. Your phone data may not seem important but think of what it contains - photos of friends and family, your phone book, calendar, cached emails/websites/texts/call history, eBooks, music preferences, etc. Everything someone would need to determine if you are worth being targetted and the information to do it.
The solution: Use your A/C adapter and carry it with you. And if you only have USB as an option such as a public charging station, a stranger’s laptop or battery pack, train/airplane/rental car USB, then use a USB ‘condom’ which physically only has the circuitry to carry electricity for charging and not for data transfer. Today I bought a SyncStop as a sort of brand loyalty since I remember when they first introduced the idea / created the market. However, for the same price you can get 2 of its competitor PortaPow.
Revisit my rants on personal privacy @ Mighty Fine Tinfoil Hat You Got There (The ‘What’)