All screen images have pixels; it's just that most have some smear or crossover with the screen material that is used that makes them looks smoother in the transition from pixel to pixel. That's why you can have a large projection or display image even at lower than SD resolution and it not matter so much for effect. The image might not be sharp but it looks like it flows together.
It's a little different with LED screens, each Pixel is separated by a distance and there are exact points of light with blacked out boarders around the light. This is great for contrast but makes your brain work harder to make the image come together as one. With the correct distance from the screen the LED lights start to converge together just like other screens to the point that your eye sees them flowing together. (Rather than individual lights) This distance is the key to having a good image with LED screens.
When looking at Video Walls, LEDs or Projection you need to think about a few things, mainly what type of coverage do I need, how much ambient light is present, how big of an image is needed for the effect I'm looking for and will it be in the camera shot? We can't get into all of these details in this article but we can at least say that knowing what you want to do and the environment you are doing it will make the other choices easier. For instance if you have a tone of light onstage or coming in from windows LED screens might be a great choice. But if the image will be in the camera shot you might want to use a video wall with monitors or projection as LED walls can create a Moiré Effect.
Another consideration for video walls and LED walls is they will need serviced, so how are you going to support them in a way to still have access for service. This is a big deal as it can really change what you're thinking. Obviously Projection does not have the same issues but there are things like ambient light and sight lines.
It is simple math to see that you can cover a large area cost effectively with EP (projection) and if you can get away with it it is definitely the fastest easiest way to go. But as soon as you turn on the stage lights a lot of that image on stage gets washed out, so looking at other options is clearly the way go if you are needing things to be dead center stage in the middle of all the lighting.
What about mixing them all together like a hybrid? Yes please, I love the look of multiple types of screens working as one, you can do some really interesting things and cost effectively augment the perception of a large screen by using the expensive equipment where it's needed (like bright areas) and then surround it with projection all running the same content from a video server. This helps to create the magic that we all want for our space.
When you looking at a solid wall of LED, a wall multiple screens spaced out, or covering the whole wall with projection, you need to first think about the big picture and how you want to use this technology. Sometimes you don't need to have the highest resolution or the brightest projection to get what you need, if you plan it out correctly.
Content is everything; no matter how cool or how big of a wall you want to make, if you don't have a plan for content your missing the boat.