Originally Posted by umeng2002
Good point. But why would some devs do it at all?
Some games run at 200 fps just fine, while some others' physics engines break down.
Other than a physics engine limitation or non-existent optimization, are they're other reasons why a cap is needed at all?
Even with the new Forza game, the Digital Foundry video said that the devs told them that the engine was optimized for 30 fps and that even on the PC, hitting 60 fps would be hard. It makes no sense, really.
Game developers sometimes use from third party physics/game engines because it's a lot cheaper than making their own engine as well as possibly having a majority of employees who are familiar with that engine. Those engines are usually for consoles only where devs choose graphics over frame rate, so the engine coders don't usually code their engines to be able to handle more than 60fps, possibly to save time and money.
Using Forza Horizon 3 as the example you provided, there was no plans on bringing it to PC until pretty recently. They haven't had time to fix the engine to run properly at more than 30fps. Physics-wise (at least with Horizon 3), there are no problems running it over 30fps, just the sheer amount of power needed. I think the only way to get 60fps+ in Horizon 3, you would need a GTX 1080 or better at 1080p -1440p or a Titan XP at 1440p-4K or higher without sacrificing the visuals.
I'm not entirely sure why the Mafia 3 devs did lock it on PC at 30fps since they were planning on bringing it to PC from the start. The devs haven't confirmed what engine is does use, but a lot of people are guessing it's the same proprietary engine as Mafia 2 with improvements, and Mafia 2 ran perfectly fine above 30fps.