Well, for example, I go from Zone 1 (Euston Station area), to Richmond (zone 4) for work every once and awhile. My final destination is a bus ride away or 25 min walk from the Richmond station. So my journey takes about 1.5 hours, and is not cheap during peak times!
So I go, tube down to Waterloo or Vauxhall, then overground train to Richmond, then bus to final destination. Its a lot of switching....and as I mentioned not cheap.
It might be different for you, if you go only on the weekends (off peak times), price-wise. But its not a straight-forward journey. You can't just zone out cause you are changing around so much. Its not for me, but others may not find it as bad. I just find it hectic being at Waterloo in the mornings during rush hour. Not how I like to spend my mornings.
M