This is a question that many new 3D modelers likely have, "What is the problem with ngons and triangles, and why do I always have to re-route my geometry to create a quad?" Yes, ngons and triangles usually get a bad rap, but there's good reason for it. While re-routing the topology on your model can sometimes seem like a tedious task it's usually worth it and your model will be much better with a little cleaning up.
What is an Ngon?
If you're unfamiliar with what an ngon is let's go over a very quick review so you can understand this question a little more. An ngon is a face or polygon that is made up of five or more sides or edges connected by five or more vertices. Anything over a quad (4 sides) is considered an ngon.
What is a Triangle?
The triangle is something you probably already understand and that is a face that consists of just 3 sides or edges connected by 3 vertices.
Right in the middle of these two polygons is the quad, which is a face or polygon made up of four sides or edges connected by four vertices. This is the polygon type you've probably heard is the one you should strive to create. However, as you're adding edge loops, resolution and shaping your geometry into what you want to make it's almost impossible not to run into a few triangles or ngons.
So why should you spend the time to re-route your topology and create a quad-based mesh? Let's go over a few of the main reasons to avoid ngons and triangles.
Ngons typically cause a lot of issues when deforming the model. If your model is going to be passed down the pipeline to be rigged and animated, then a quad-based topology is a must. Triangles can also cause this issue. While triangles are a little more lenient and not as bad as ngons, they still can cause some issue at animation time.
Topology that isn't clean means a model that is going to be sent back to you for fixes. While you may be working on your own project, and you're the modeler, rigger and animator you certainly make your own rules during the modeling stage. But you'll quickly find out first hand the issues that arise as you try to animate an ngon heavy model.
Ngons and triangles can also cause some strange issues at render time. While everything may look good in the viewport, once rendered you may notice some very strange artifacts happening. The only way to really avoid this is to go back and clean up the ngons on your model.
Ngons and triangles both cause issues when trying to smooth a model. The extra vertices and edges can cause some very strange bumpiness in the model that would otherwise not occur if the model was made up of quads.
Quads Are Accepted in Every Area of the Industry
A very important reason for avoiding ngons and triangles is that quads are really the industry-accepted polygon. If you send in a 3D modeling demo reel with a wireframe overlay and your model's topology is made up of a miss match of quads, triangles and ngons of all different edge amounts then the message you're sending the recruiter is that you don't spend the time to properly topologize your model to work within the other areas of the pipeline like texturing, rigging and animating.
There are certainly instances where ngons can be used, for example on a perfectly flat surface, and times when triangles simply can't be avoided, or maybe you can hide the triangles at a place that the viewer is never going to see them. But you should try to spend the time to clean up your model and re-route any problem solving polygon types into quads.
If you have questions that you want answered be sure to post them in the comments below!