That being said this is useful even if it wasn't for the running AI agent code aspect, being able to limit ram and cpu usage and time outs makes it easier to run coding based games/applications safely (like battle snakes and Leetcode)
I made a small example that might give you a better idea (it's not eval, but shows how to isolate a specific data processing task): https://github.com/mavdol/capsule/tree/main/examples/javascr...
And yes, you are spot on regarding LeetCode platforms. The resource limits are also designed for that kind of usage.