The various player dialogs, such as "Set Players Paid in Full", "Buy-in Players", "Undo Player Buy-ins", can all be invoked with hotkeys. So I usually recommend this:
Buy-in everyone who you THINK will be attending, and seat them. After that, you can remain on the tournament page, or the seating chart page, if that's helpful. When players pay you, bring up the "Set Players Paid in Full" dialog and mark them paid.
After everyone who is going to show up does so and pays, bring up the "Undo Player Buy-ins" dialog. Click the "check not Paid in Full" link at the bottom, and everyone who hasn't been marked Paid in Full will be checked. Then click OK. This removes the buy-in for those players that haven't actually paid, and unseats them (there is no separate step for unseating the player - a player can't be seated if they haven't bought-in, so undoing their buy-in does both).
Finally, press Ctrl+T to balance the tables. Tables *might* be out of balance if enough players didn't show.
No need to jump back and forth between screens. If you didn't modify "buy-ins" because someone didn't show, you'd still have to unseat players who didn't show. It's six of one, half-dozen of the other.