Quickee. I’ve bought myself my first tubeless tyres and fitted them to tubeless compatible rims.

Do I need to pour in slime/latex liquid/similar gunk?
Or is it just recommended to reduce punctures?
Or is it entirely unnecessary?

Use it – not worth the hassle of not bothering

It’s recommended. It forms a good seal at the bead so there’s no hassle inflating the tyre, no air burps on the trail. Will also seal any small punctures you might get.

It’s not absolutely essential – I have a UST tyre on the front of one of my bikes without any sealant in as I ran out recently, and it’s riding fine. Over the years though I’ve had better results using it.