30ms is close to extremely annoying. You will notice a 30ms latency in a video game when moving around, turning etc.
Having that kind of latency on mouse movement can make it close to impossible to hit fast targets in a shooter for instance, because it will destroy perceived synchronicity of input with the response, confusing your brain and destroying immersion.
The same can be said about navigating in a terminal based text editor. A few milliseconds of delay can take your brain from "I am the cursor" to "I am controlling this cursor, which respond a short time after I execute a certain action". Frustrating.
What is also super frustrating to me when using vim in a slow terminal is that I will consistently overshoot the line where I meant to place the cursor. I realize most of the latency probably comes from my brain and nervous system, but a few ms can be just enough to make the cursor end up in the next line instead.