I can see the advantage if you have limited mobility and if you were in the older age bracket, how easy it would be getting on to a ship, unpacking once and having the world come to your door.
There would be no airports, no transfers, and no finding a hotel!
There is always a downside though, you would not want your cabin to be windowless as that would not be fun, you would not want to get seasick, and would boredom eventually set in?
Staying connected with family, especially grandchildren could prove to be a bit difficult, but no more difficult than having your family live overseas, I guess.
You will also have to hit the onboard gym regularly if you do not want to put on too much weight from the wonderful onboard food!
When it comes to the cost of living on a cruise ship, it is going to depend on how you choose to live, just like it would on land. For example, what cruises you book, the food plans you choose, and how much entertainment you buy, will all vary with each person and could impact your overall costs. Many find living this way more affordable than paying off a mortgage!
If thinking about making cruising a permanent idea, it might pay to take an extended cruise to make sure you want to make this a permanent retirement option.