Cyclopes is a great example of how to make pops an interesting feature of the game.
Bottom left pop replaces a slingshot - makes the ball less predictable at the flippers
The upper pops obscure direct shots to targets. Upper flipper used to shoot through the pops for drop target hits.
Here is a good video of it in action: https://www.twitch.tv/videos/496878739
If you skip to 1hr 8min mark, you can see Roger Sharpe show us how it's done!