Inspector panels are really useful for furnaces.
With inspector panels, you are able to detect if a furnace is out of fuel. This is useful because you can have a logic gate 'connected' to the inspector panel that can allow for fuel (such as chocolate fossil) to be inserted into the furnace. I really haven't found any other uses for the inspector panel.
Logic gates are one of the most useful items in the game.
The majority of my earlier designs use logic gates. I used them to detect when an object is created from any machine and allowed for its crafting items to be inserted into the machine. Just make sure that you do not run out of a crafting item, as if you do it could potentially ruin your whole setup. I suggest over-producing items for all your setups, and any overflow just destroy it with a trash can.
Please let me know if you have any questions with what I said (or anything else). I want to write a guide for this game after the update gets released, as this game is honestly an 11/10 but I know some people are not familiar with factory games so any feedback will be appreciated.