I keep the pace down as a warmup at the start of rides and I also try to stay in zone 1 in the last mile+ of a ride. I do live on a slope, so sometimes I ride past my home so I can get level with it, some distance away and therefore keep the power down in the last minutes of the ride.

I don't know if this has any sort of fitness benefit. Though I think it does as moving the legs would seem to help circulate blood and perhaps help to clear out the byproducts of harder efforts. What it does for sure, is actually help me cool off. If I don't do the cool down, I become a sweaty mess as soon as I stop the bike. If I cool down while moving, the sweat continues to dry off and I'm in fact, cooled down quite a bit when I do stop.

As for post ride protein, what I've read or seen lately on the inter webs is an immediate post ride protein intake doesn't help specifically. I.E., the timing doesn't matter. What matters is getting the protein in at some point that day. So, I too have a protein shake. But I don't necessarily make a point to have it soon after the ride. Though sometimes I do.

I'm also old enough (63) that I have a protein shake every day, whether I ride or not.

But I have heard getting carbs in within the first hour after a ride, improves building up glycogen stores. Basically, that within that first hour, your body is primed for replenishing glycogen. Also, this is another reason to eat while riding. Even if the eating doesn't help that ride, it gets you a head start on the recovery.