There are a few times when the journey planner suggests changing at Basingstoke on a Southampton - Waterloo journey. Of course it's often a good idea to catch the XC up there and then change on to an Exeter/Bristol - Waterloo train, but the arrival into Waterloo is sometimes 1 minute before the direct Southampton - Waterloo train, which leaves Southampton 15 minutes later and avoids a potentially dodgy connection at Basingstoke.
Much the same in reverse: the 1820 (to Exeter) is suggested as sensible departure from Waterloo to Winchester, changing at Basingstoke to pick up the XC service. It's a pretty big gamble, though, as the connection is very tight and if the 1820 picks up a delay, you'll miss the 1910 out of Basingstoke. And of course the 1835 ex-Waterloo is first stop Winchester.