The Conservation of Matter
The game respects the concept of the conservation of matter. If this was obvious to you, ask the people who asked me this question what they were thinking. The point is, this concept brings the conclusion:
The limits to your ouptut is the amount of substance that runs through your factory.
The amount of substance used can usually be used to evaluate how good a factory is just as well as the output.
Seriously, that's it so stop trying to increase output while reducing substance input
The Throughput of Devices
Every device in the game has a limit to the items it can transport or convert. This is crucial when identifying your bottleneck (further info found in the debugging section). Here is a table of values:
