I've seen "Absent" buttons used when a player's stack of chips is on the table, but the player isn't there. Some dealers are taught to "deal to the stacks" (of chips) around the table, and they might deal a dead hand to the absent player, which messes things up. An "Absent" button in front of the stack of chips reminds the dealer to skip that position when dealing.

In contrast, the "Player Returning" button is often (not always) used when a player has lost all his chips, but is planning to return and play more. The button locks up his seat. It's functionally the same as a "Reserved" button.

I haven't seen the "Present" button in use.