[microtonal]

It depends on the application. For instance, in search engines approximate matching is very useful. E.g. if people want to search for Rotterdam, they make typos like Roterdam or are foreigner and don't know that Rotterdam has a double t.

You can rank candidates afterwards. However, it's a good solution for finding words that are closed to a mistyped word.

I have successfully used such techniques in a spellchecker and various search engines.