Traveling is absolutely one of them! You're making getting a local SIM sound much more difficult than it is; even in places like Germany the process is pretty quick and most places aren't anything more than give-currency-get-card. It's also very convenient to have a local phone number as many people are not excited about making an international call to tell you your table is ready (the alternative here is being forced into the panopticon of WhatsApp). It also encapsulates the trip nicely, nobody I give my number to while I'm there can call me when I get home unless I give them my real number.