I'm more familiar with living in countries other than the country in which your income is derived. That means you always have to be aware of the potential affect of exchange rates.
For example, a grea many Brits who retired to Spain and then saw their income in UK pounds sterling drastically affected by the exchange rate with the Euro have been moving back to the UK because they could no longer afford their 'villa with a pool' in Spain. Most of them got into trouble because they were living on or near 100% of their income and had no 'cushion' of income to absord any major fluctuations in currency exchange rates. They went from comfortable to poor in a relatively short time.
Another example is the exchange rate of the UK pound to the Canadian dollar. My wife's employee pension got her $2 CAD per pound when we moved to Canada 8 years ago. It has been down as low as $1.58 and only recently started moving back up. So she saw a reduction of almost 25%. Fortunately, it is an index linked pension and that made up for it each year to some extent. It's a bit frustrating though when you get a 'raise' in your pension and all it does more or less is keeps your 'local' income at the same level.
We are also fortunate in that I have Canadian generated income, our entire income is therefore not affected by exchange rates. But mine was when I lived in other countries.
My point then is that if someone plans to move to another country after retirement, they need to realize that exchange rates is something they are always going to have to deal with and plan for. You can't control it so I would not plan on living on more than 75% of your income at most initially.
Another factor that can affect early retirees who leave their home country is the impact on government pensions. I don't know about the US but in Canada for example, the government OAS (Old Age Security) pension is based on years of living in Canada after age 18. To get the full pension you must have 40 years of residence. Someone retiring at 50 and moving to say Costa Rica(example only) will not get a full pension when they reach age 65 as they could only have a maximum of 32 years residence after age 18 if they moved at age 50. That comes as a big surprise to some people who have never looked into the consequences of leaving the country.
The UK is similar in needing a certain number of years of contributions to qualify for a full government pension.
Health care is another factor when considering retiring in another country. In the US you are used to paying through the nose for healthcare. In the UK, it's free and in Canada it's next to free. A family living in British Columbia gets full health coverage for $130 (2 people) $144(3 or more) CAD per month. Someone retiring to another country needs to take that into account. I've seen retirees complaining bitterly about how much healthcare is costing them as if they didn't know beforehand what it was going to cost.