This is proper posture. Not doing it means you use your shoulders to position your head as opposed to your neck. This puts strain on the entire spine. 

Forward head posture can be quite damaging. 

It's fine to go with some force until the relevant musculature in the neck both loosens and strengthens enough sufficiently to maintain that range of motion so that you only need to lift the head lightly. Ideally the back of the head should be aligned with the spine, and they both should be centered around the area between your heels (standing).

Loosening the neck too much increases risk of chronic and instant injury to the upper verbetrae, but proper tongue posture should prevent this from happening.

I think that it is definitely essential and that you should do it all the time because it is proper posture. So asking if you should do it all the time is kind of like asking if you should have proper posture all the time. Ideally the answer would be yes.

It's pretty related to doing a chin tuck, they are almost the same thing. I usually envision it as pushing my maxilla against my jaw while doing a chin tuck. Going into this posture helps with mewing with the tongue as well.

CP actually talked about this a while ago and you can check out the article here if you want:

https://archive.fo/oVptM

The first picture on that article really lets you see the head rotation that is needed for good posture.

Thanks for the replies. I kind of knew it was an essential part of mewing, I just didn't prioritize to it as much as I do for the tongue and masseter muscles. 

When I do lift the back of my head, I can feel a bit of strain in my lower back. Is this normal?

Thanks

There's no such thing as normal. Every person's body is going to react differently based on their own unique anatomy and history. I only bring that up to make you aware of the idea that you are going to have to do a lot of your own troubleshooting in the future as you explore this topic more deeply.

Anyways the lower back strain sounds to me like a posture issue. Try letting your shoulders go back some more and make sure to squeeze your abs as well. Alternatively, you can try lifting the occiput while standing with your back  and head against a wall. If you continue to run into random strains/pains while experimenting with your posture then you might benefit from taking up some form of whole body exercise.

Lift your occiput and then move your neck back. Don't look down. Your eyes should be looking straight ahead. 

Post a side pic or full body profile if possible

So, unless I'm mistaken, I am supposed to lift the back of my head using my rear neck muscles, and while doing this I need to do a chin tuck? And this is how I should always posture myself? Sorry if I keep asking questions, just making sure I am on the right track. Thanks.

Posted by: Matt

So, unless I'm mistaken, I am supposed to lift the back of my head using my rear neck muscles, and while doing this I need to do a chin tuck? And this is how I should always posture myself? Sorry if I keep asking questions, just making sure I am on the right track. Thanks.

I short, yes. Although like mewing you can do this actively or passively. Actively lifting up the back of your head as if pulling it up with an imaginary string while also tucking in your chin will put you in an exaggerated version of this position that you can try to sustain for increasing durations of time, for example while driving in a car with the back of your head against the headrest. It's also good to be mindful of your tongue's contribution to holding your head up in this position (especially the posterior 1/3). The more you practice this active exercise the better your passive posture will become. 

I have noticed using this method really improves my posture, my front profile and I can see my neck muscles being really worked. Although, for some what reason, my side profile seems to become recessed as a consequence of using this posture. Am I doing something wrong?

Posted by: Matt

I have noticed using this method really improves my posture, my front profile and I can see my neck muscles being really worked. Although, for some what reason, my side profile seems to become recessed as a consequence of using this posture. Am I doing something wrong?

Consider it like this: your head is close to its correct neutral position and tilt now. The amount of recession you can perceive while in that posture is therefore a good approximation of how long journey you have in front of you. Most here relate to your problem, as proper head posture will not be an aesthetically flattering position unless your face is already well developed.