Basics of Local Rotation Axis in Modeling

Freezing Transformations: When? Why? ect...

When you freeze an objects transformations in maya, you are essentially creating a new start point for that object, replacing all of its translation and rotation values with zero. At face value, the concept is pretty easy to swallow. 

However, there are times when this feature is helpful, and there are times when using it is a really bad idea. Learning the importance of maintaining coherent object orientation really sped up my workflow, especially in set modeling. 

BASICS OF OBJECT ORIENTATION

1. If you maintain rotations that make sense, that object will be much easier to modify later, if needed.

Lets say you have a box. 

You place this box at a random angle, and freeze its transformations. It automatically reassigns Z as forward in world space. Z no longer represents the front of the box.

Now you decide the box needs to be longer so you scale it along its Z axis... its not a box anymore. 

Since the Z axis has nothing to do with the front of the box, you can no longer simply scale the object along its axis without distorting it. In addition, sliding edge-loops, extruding, and countless other modeling techniques are much more difficult with poor orientation.

In order to fix this problem without pressing undo (you trickster), one could realign the object in top and side view to the grid and then freeze its transformations again.  More often than not, I use FT to fix an object with a weird local rotation axis.

The first, and most important thing to keep in mind in regards to your object's axis is to making sure that it agrees with the objects actual shape. That way to scale along Z, you can do so by setting your move tool to object mode, regardless of its rotation.

2. Freeze transform can be used as a "home base" for an object, so it can be pulled out of a section and worked on more easily.

If your objects placement in the scene happens to line up perfectly with the grid, it's fine to freeze its rotations. Then you can grab that object (or group) and move it elsewhere for modeling or making a quick change. Once you are done, you go into the objects translations and zero them out, it will go perfectly back into place. Its like the old school way to "isolate selected".

Even cooler though, is in the option box for FT. Often I turn off its ability to freeze my rotations. In doing so, you get the ability to freeze transformations, creating a new "home base" for that object, even if it is askew. You can pull it out and work on it elsewhere, and zero it out to send it back.

3. You can lose or fix an objects local rotation axis by modifying it on a vertex level

Often a coherent axis is lost because the shape that is being modeled is organic, and in the heat of modeling, it gets skewed on a vertex level. Keep in mind that if all verts are selected and the object is rotated, its local rotation axis will not move.

Likewise you can fix the rotation axis of an object by moving its verts in the same way.