This run through, I'm focusing on trying out things I've never used before. I'm at a loss on the Presserator, now that there is a Grand Design. Granted, you can luck out and get the Presserator earlier than you can get the Grand Design, but before you rescue the Mechanic, I don't see any point to having it.

In what cases would it be better to place actuators when installing blocks vs. when installing wire?

There are many redundant tools and items, and quite a few of the things you can get from the Travelling Merchant falls into that category.

The Presserator and The Grand Design do different things. While you can set up TGD for a similar effect, the Presserator automatically places the actuator on the block when the block is placed, as opposed to TGD which would require a separate click on the object with TGD selected. It's a niche item for sure but I wouldn't say it's strictly redundant. It'd be a time-saver if you're building large actuated areas, especially if those areas are already wired.

That said, I don't think it's a very useful item. It's hardly detrimental to the game, though.