If so, why would one want to do that? Are there reasons to consider having?

Yes. I had one when I was an expat.

It was great when I was there, but a pain in the ass after I repatriated. Fortunately, had a business trip back about 18 months later and closed that thing.

Yes. There are reports that one must file about foreign accounts though.

One reason might be to hold funds in a jurisdiction with stronger liability protection. Another might be to more easily invest in foreign currencies. I guess some folks like to diversify their life so that all their eggs aren’t stuck in one country.

I wouldn’t mind having enough loose cash to worry about such things.

One big reason NOT to is if you hold a clearance. It's still not against the rules, but anything that holds up your investigations is a PITA.

The benefits are numerous, for example, living here, if I want a fast pass for tolls, gotta be attached to Korean Bank, one of the bullet trains only allows online payment from Korean Banks, many delivery services, apps, etc etc. It's way more convenient, so if I didn't have a clearance I would definitely open one.

You don't necessarily have to live overseas either, simply conducting business abroad present numerous scenarios were a local bank is better.

Yes, the only problems are IRS reporting of stipulated foreign assets over $200,000/$300,000 or jointly $400,000/$600,000. Foreign bank deposits in treaty countries are reported to IRS. Residences & rental properties are one of the asset exclusions. Also bank transfers can be difficult if your local banker is not familiar with foreign wires. Wire transfers are easier if you have a US account with a bank that can do direct transfers such as BOA or Citibank. Many foreign banks have US Dollar accounts so exchange is not needed.

I had one in Germany while I was stationed there for my cell phone/ internet service. It’s not a problem

Make sure you properly report it to the IRS on your 1040. People get hammered hard for not reporting even perfectly legally obtained assets domiciled offshore

As others said, yes, it's legal. You can open an account for whatever reason you want like having a Swiss bank account. The simplest reason is if you go to a particular country quite regularly or for extended periods of time.

It is a question asked on the Form 1040 Tax Return.

Additionally, you have to file Form 8938 if you are unmarried with assets more than $50,000 on the last day of the ax year or more than $75,000 at any time during the year. Married threshold is $100,000 / $150,000. Those thresholds are if you're living in the US. If you're residing outside the US and file US returns, Single thresholds are $200,000 last day or $300,000 any time of the year. Married - $400,000 / $600,000.

Separate from the IRS requirement is the FBAR requirements if the total value of all foreign accounts exceeds $10,000. It's filed separately and not part of the tax return.

I know this because I was planning to live outside the US until my Social Security Full Retirement Age. But Covid stopped that. And I'm actually glad Covid happened before I left the US. My wife and I would have been miserable in the country we were planning to move to once Covid hit and the lockdowns began and oppressive populace controls were put in place.