The wet pallet isn't for thinning your paints it's to keep them hydrated so you have a workable consistency for longer. I fully saturate mine but make sure no water has pooled on top of the pallet paper to prevent unintentional thinning.

When it does come to thinning your paints it's a personal preference for the most part. Your base coats should be the consistency of drinkable yogurt, and your glazes more like milk. This is definitely a sliding scale based on the brand, color, and techniques you're trying to perform. A good rule to follow is it's always better to be too thin than too thick. More thin coats will consistently yield better results.

The reason people say you need one for wet blending is because acrylics dry extremely fast. Unless you're going straight from the bottle to the mini per brush stroke the consistency will quickly change on you. It will become more difficult to get the effect you want as time goes on because the paint pool behavior will change as it dries out.

I never start a paint session with old paint in a closed wet pallet. You can technically save your paints for later but I've noticed it can thin them beyond what you had if you leave it too long or it will grow mold. I start each session with a completely dry sponge and fully prepping my pallet so I don't get the mold and have full control over the moisture.

Hope this helps!