Many post state the importance of letting your bank know of your travel plans. I work for a major bank and get calls daily with people upset that they are on vacation and their card gets blocked. The reason is, in recent years, identity theft is on the rise and when your card IS used fraudulently, both the bank and possibly the merchant are out the money. Which they pass on to us.
Also, by letting your bank know of your travels,they can let you know which atms you can use to avoid fees and what the international conversion fee is. Some travel credit cards the fee is waived.
Even if you don't plan on using your card, you are taking it for a reason,, emergencies so its a good idea to let your bank know of your plans including any layovers.