The stronger dilutions are typically used for alternative process negs to achieve the higher contrast needed within some normal development time. For example, I use 2:2:100 when developing for pt/pd prints.
Also, since A is essentially the developing agent and B is the accelerator, some folks play around the the standard dilutions to achieve some specific goal. Personally, in all the years I've used Pyrocat-HD I've never used anything other than 1:1:100, 2:2:100, or, more recently, the diluted mix used with Steve Sherman's EMA process. It's actually pretty versatile stuff; Sandy King once told me you could probably go to 1:1:400-500 and still get good negs.