Tbh most of the interesting retirement planning problems are in planning for life events along the way.

The advantage of proper modelling solutions like Voyant is that you can see your cash flows across your entire life and see what happens long term if you pay down your mortgage by 10% more or 10% less for the next few year, or if you add a change in 5 years time where you start paying £1500/mo for childcare

I'm currently slamming my pension for example because I know in the near future, if I have kids or remortgage (due in 3 years), I won't be able to afford to do so (on my current salary)