If visiting a city centre location then trains are great. If you need to get to a place near a city then trains are the worst, at least airports tend to be outside of the city near the arterial routes.

I am originally from the outskirts of Glasgow and now live on the outskirts of London. For my partner and I to get to my parents house by train takes about the same time (assuming all 4 changes go according to plan), costs 6x as much and is far less flexible than driving. We tend to stop at a cheap hotel midway so we can set off after I finish work.

One trick to driving into London is finding a parking space at a station outside town and continuing on TfL services. E.g. if you are coming from the M40 park at Hillingdon Station.

But often the reverse is true - if your meeting isn't in the middle of London, it's much easier to drive directly to the place than get there by changing trains. This applies even more if your destination is a smaller place.