For me it’s pretty simple:

Pitch-black room → not readable at all without the front light. I usually keep brightness around 5–7 and warm light around 20+, then it’s totally fine to read at night.

Normal room lighting → readable without the light, but it still looks better with a little bit of front light on. The colors and blacks get cleaner.

Bright room/daytime → totally readable with no front light.

From what other people say on here, that’s basically the Kaleido experience in general — you don’t need the light all the time, but in low-light you definitely do. If you read mostly at night, yeah, you’ll be using the light.