When dewpoints climb, like in the summer, humectants can pull too much moisture into the hair, causing it to frizz and get poofy. Even without humectants, hair can poof in high dews. In that case, especially for people with high porosity hair, anti-humectants (like oils) help seal some of the humidity out while simultaneously sealing moisture in. So, the hair is already well moisturized and doesn't need to reach out for more. In low dews, like in winter, the air is drier than the hair and humectants can pull moisture out of it, leaving the hair dry and frizzy. In that case, anti-humectants can help seal moisture in and keep it from escaping as easily as it would otherwise. So, hair stays better moisturized.
Protein is what gives hair structure. People with fine textured hair (small individual strands) generally need to use protein in products to give their hair needed strength and weight. People with coarse textured hair (large individual strands) generally already have an abundance of protein in their hair, so they'll concentrate on moisturizing products to give their hair better flexibility (if that makes sense). This doesn't mean that they never need protein, only that they require it less often and in smaller amounts than others would. People with medium textured hair (in between sized individual strands) can use products with a mix of moisture and protein.
Porosity also plays a role in how much protein someone needs, though maybe not quite as much as texture. High porosity hair is often from damage (coloring, perms, heat) but can be simple genetics. It has a wide open cuticle, which means it gets wet and dries quickly. Even though well moisturized during and directly after a shower, it may get dry by the end of the day. High porosity hair can greatly benefit from protein because it helps fill in the open spots in the cuticle which allows it to hold onto moisture better.
Medium porosity hair has a cuticle that isn't too open or too closed and is middle of the road in terms of protein needs.
Low porosity hair has an overly closed cuticle, so it takes a while to get wet and a long time to dry. Heavier products can sit on the surface instead of absorbing, leaving the hair feeling producty and looking weighed down. It can take some encouragement to get it to accept moisture (or protein), but once absorbed, it hangs onto it. A little gentle heat and/or some additional time are both good for enhancing absorption of product into low porosity hair, whether it's protein or moisture. Some people like to use baking soda (a base) to open the cuticle, then pt or dt because the more open cuticle helps their hair better absorb the pt /dt. Afterward, an ACV rinse will close the cuticle back down, helping to seal in the good stuff they just added into it.
In this case, once you know how to get things to absorb well, it's helpful to look at texture to see what you need to give the hair. Fine, low porosity hair may like a good amount of protein. I know mine likes daily protein and a pt every couple of weeks. Coarse, low porosity hair may prefer daily moisture, and dt's every so often. Medium textured low porosity hair will need a mix of protein and moisture.
If you don't know your texture or porosity yet, this page is a good reference: Live Curly Live Free - Curly Hair Basics