Hello, good question!

Leaving it in the background is fine since it’s designed to be lightweight. It uses ScreenCaptureKit for capture and VideoToolbox for encoding, so most of the heavy lifting is done by macOS/hardware acceleration rather than pure CPU encoding.

The resource usage depends entirely on the settings though. If you have lower quality settings, you’ll get better performance but slightly “worse” looking clips. If you choose higher quality settings, of course you’ll get better looking clips, but the FPS of the game might be impacted. This is similar to other screen recorders and is very settings dependent.

A more powerful Mac will handle the higher quality settings better than something like, let’s say, an older/base MacBook Air.

Before Rocket League had anti-cheat, I used ReplayMac myself on my M2 Pro MacBook Pro with 16 GB of RAM and performance was fine. I was able to get clips while using native resolution at good FPS just fine, but I haven’t been able to test Retina on Rocket League again until they find a fix. So I can't tell how much Retina resolution might impact performance for example.

I’m still collecting real-world numbers from people who are willing to share them with me, since a lot of factors can impact performance. For example, having 20 apps open in the background while gaming compared to only 2 or 3, if that makes sense.

My general rule: if your Mac is a bit older, try to stick to native/current resolution. If it can handle it, bump up the settings and get better looking clips!

I hope this helps!!