Definition
If there is a natural subsystem that supports it, there is value on it.

The biological systems corollary
If any species has a biological subsystem that supports it, there is value on it.

The biological opposite corollary 
If it establishes an opposite force to a supported biological subsystem, there is value on it.

The group corollary
If it creates a force that is convenient for a group of individuals, there is value on it.

The movement corollary
If it creates continuous repetitive stimuli well received by a group of individuals, they will integrate their sense of identification with it, so there is value on it.

Plausibility arguments
Instead of demonstrate this, I'll merely do what I can by mentioning the plausibility arguments I've found so far:

1. Energy. Biological systems have an efficient use of energy.
2. Function. Healthy biological structures are evidence of something that works well. 
3. Persistence. Everything that lives has passed the test of time.

Applicability
The natural convenience principle makes you able to evaluate the designs, of anything you and others do, with questions like this:

In which degree is this design creating a context that is received as naturally convenient for a group of individuals?

Clarifications
  1. The semantic use of the word design here is quite broad. This assumes that anything can be designed: a work, an artifact, a piece of software, an experience, an initiative, a product, a performance, a service, a political movement, anything. Whatever you can premeditate or be the author of.
  2. The use of "it" was intentionally left abstract so you can plug there anything you want. That way you can evaluate everything under the lens of the natural convenience principle and see how it scores.
  3. The functional use of "value" in the definitions is clear but the definition of value itself was left open. That's intentional for the same reason as before. That makes you able to plug there any value equation or value system you want to use. What you are considering valuable is up to your mindset.
Consequences
The best way to explore the consequences of the natural convenience principle is to start a discussion about how well known things can be evaluated with it. I have to do that in another post.

What I wanted to mention about consequences near the definition itself is this:

The natural convenience principle, when intentionally used, can have a crucial role in defining the value of anything that can be made. Also can be used in estimating its consequences. In particular, you can use it to define the value concentrated in a design. That can greatly improve the chances of making it to be naturally selected and spreading capable which is crucial for success in the long term.

So this principle can be applied to any field. Here is a small list to give an idea: graphic design, industrial design, ad agencies, architecture, user interface design, human computer interaction, engineering, arts, experience architects, screenplay, photography, copywriting and I'm sure you will find more.

Note that you can count the number of hooks to the principle. The hooks are the features that you can connect between the design being evaluated and the natural convenience principle. If you want to design something memorable, if you want to leave a legacy, you need as much qualified hooks as you can provide.