This entirely depends of the application. In combination with backface culling coplanar faces with opposite normals (like in @mano-wii 's example) definitely have their uses, especially in game engines.
The mesh from the example is not an invalid mesh, though it might be an undesirable one depending on the application.
It just doesn’t make sense. I mean if you wanted that result you would not use extrude boolean, you would just use regular extrude which would produce that very same result. The whole point of having a tool like extrude boolean is that it does not produce such results. That it explicitly avoids them.
There is no Z-fighting either:
A believe a new build must be already available for testing:
Ohhhh… Ok, nevermind, I completely misunderstood what was going on. My bad!
First a big thank you for working on this. It’s great, but could be even better 
.
This case fails no matter the settings.
Example 2 - the subtracted circle is coplanar with the top
with inverted
One more thing - not exactly problem with the extrude boolean but weird still.
Two columns, boolean extrude without Remove coplanar faces.
Thanks for testing @cdog!
I had even fixed the first point locally.
The second was by a design created before the “Invert” option. But in fact, there is no longer any reason to keep the first group of faces. So fixed now
According to the blender-coders chat, there was an outage right around the time that you posted this that might have caused the issue with the CDN preventing you from downloading the build for testing - I’d just try again at this point and if it’s still misbehaving let us know so someone can look into it further.
Just tested it out, and it works great! Thank you for your hard work on this tool;
Very useful!
I’ve noticed that turning Invert off and on alters the result.
It’s great to be able to extrude in XYZ too, nice addition.
This should have been fixed by now.
But I’ll keep an eye out. Thanks!
Thank you, I managed to download it after a few tries.
I just tested it and got the same behaviour, switching Invert on and off a couple of times will change the result.
Other than that it works great, much better than Extrude Manifold in most cases
Hi, when will this amazing feature be implemented in Blender? Has it been abandoned? Sorry for the silly questions!
We’re still waiting for proper Push Pull like sketchup
I’m currently away from coding due to health issues (I’ve been undergoing treatment for a few months but I’ll be back soon).
One thing I still intend to improve/rework is the code for detecting intersections between triangles. I’ve detected a flaw in it. And it’s the most complex and laborious part 
Will this replace the existing similar tool in Blender? The current one was pretty much useless tbh. 3ds max has an awesome implementation of this but it required lot of complex coding and world class engineers.
We have some very good engineers working on Blender as well. And while also I’m excited to work Germano’s excellent new tool, let’s realize that there are other concerns (health) that take precidence.
(Best wishes to you, Mano - I hope this ends for you very soon.)
Wishing you well with your health!
Sorry to hear that, hope your treatment is going well! Nothing’s more important than health, so take all the time you need man.
Just wanted to say that your work on this feature is seriously appreciated. ‘Smart Extrude’ is the only thing I was ever envious of in 3ds Max, it’s just brilliant. Can’t wait to see it in Blender one day, but no rush at all. Wishing you a smooth recovery and looking forward to whatever comes next when you’re ready.
Cheers, and good luck! You’re awesome! 
