On many remotes there's a jump/previous/last button that lets you go back and forth between two live TV channels.
On a Tivo the same button could do much more. Were the last two things you did both out of Now Playing? Then bounce between them at the point you left off. Were the last two things you did one out of Now Playing and one out of Live TV? Then since it's recording the current show all the time bounce between them without missing parts and fall non-steadily behind caught up. Were the last two things you did both Live TV channel surfing? Then you've lost the ability to be behind real time but you'd be able to alternate channels with a single button.
Before Tivo I used the previouos button a lot. Now I use a lot of menus but still alternate.