On/Off or Thaw/Freeze - What's the difference?

Good question. There are differences, but they are subtle. The most common use of these commands is to make data invisible but retain it in the file. Both methods will accomplish this.

Off/Freeze Similarities: Is not visible, does not plot,

Differences:

On/Off - Is hidden in 3D, is still regenerated when off, will zoom extents to OFF layers, off a layer a block is on only items on that layer in the block are invisible

Thaw/Freeze - Can thaw/freeze per viewport, will zoom extent to thawed layers, freeze layer a block is on the entire block is invisible

There may be more, but this is the basics. The main differences again are; you can thaw layers per viewport, you can't turn them off per viewport. If a layer is off, it will be off in every tab and every viewport.

If layers are off, AutoCAD still regenerates them, though there is nothing to see. Not so much of a problem anymore, but why regenerate invisible lines?

If layers are OFF, and you ZOOM EXTENTS, those layers are still included in the "extents". But if they are "frozen", then you zoom extents only to what is visible.

If you use a block that has uses layers in it, and insert it on a different layer, when you freeze the insertion layer the entire block is invisible. If you turn off a layer, all layers used in the block that are on a different layer will still be visible. Example: I have a block with a layer in it called blue, and a second layer called green. I insert the block on layer red. If I freeze layer red, the block will be invisible. If I turn off the layer red, I will still see the entire block. If I freeze or turn off layer blue, then only the objects on layer blue will be invisible.

WOW!! That's confusing. It is easier to do it yourself than to read about it. Try it out and let me know what you discover.