[taftster]

Traditional chess applications are "thinking" while waiting for you to move. That's not to say they can't be sleeping while waiting for your move, but it would just delay the game tempo and possibly (slightly) limit the overall competency of the chess AI.

[noir_lord]

Not slightly, greatly.

Speculative move generation of a chess engine on opponent time is a huge part of the overall strength especially when the engine can see a forced move therby collapsing the tree.