Mira:
The thing with a SIM card is that it gives you a new number. So you can’t receive calls or texts at your normal number, and for many people that’s a deal breaker. I need for my relatives, friends, work, and kids school to be able to call or text me. I think that’s fairly common, making a SIM card not useful for people who need to be in touch with home while traveling.
But a MiFi doesn't solve that problem, either, right? You wouldn't need a MiFi if you had a decent international roaming plan (and so could also use your phone for calls).
In any case, there are ways around not having your main US phone number available while you are traveling. One is to get a Google Voice number and use Google Hangouts to make/receive calls (even to/from landlines), free to call US phone numbers. This is how I have done it for years (only a solution for Americans, though). Google Voice gives you a new US phone number, which you would have to give to people who want to call you. If you are savvy enough, you can figure out how to forward incoming calls to your cell number to your new Google Voice number.
I have used my Google Voice number as my regular phone number for years (before I even had a smart phone), so now when I travel I don't have to give people a different number or forward anything - incoming calls ring in the Google Hangouts app and I answer them. No one calling me knows if they are calling my landline, cell phone, or whatever or even where I am.