The use of Hybrid Log Gamma (HLG) when recording .nefs is primarily for the camera to generate a .heif image rather than a .jpeg. Whether singularly, embedded into the raw file, or both.

Unfortunately, it does have some negative (IMO) impacts to the raw file, much as selecting D-lighting does. It affects the metering, resulting in underexposure just like D-lighting does for jpegs (to protect highlights). And it also increases the minimum ISO to 400, which is potentially also additional underexposure (lack of light recorded). This underexposure does affect the raw data; which results in increased noise and a reduced ability to recover shadow details, as one would/should expect. The color space is also changed to rec.2020; but that doesn't directly affect the raw data.

In order to use HLG effectively with raw files (stills or video) you need to pull the exposure up during recording in order to compensate for the raw data underexposure that would otherwise occur; and then recover in post. Because many do not understand this, there is a lot of noise currently about avoiding HLG with still photography.

Here's one example: Steve Perry's HLG-SDR video

While you can compensate for what HLG mode is doing to make effective use of it, and using ISO 400 isn't necessarily/always a negative, I do not personally see any advantage when working with raw still images... I do not do enough video work to have an opinion on that.