Layer Status

ON / OFF

When the layer is OFF, Objects on this layer are invisible, also not plot 
But you can draw, only cannot see

AutoCAD still consider the objects on the off layers
So, it regenerate the objects on the off layers

Thaw / Freeze

Layers no need for long should frozen
When layers is frozen, also invisible and not plot

You cannot make the frozen layer current, so cannot draw on it
The frozen layers are not regenerate

It's good practice to freeze the layers for hatch, text or any graphics when they are not in use, this will help to speed up the drawing performance

Lock / Unlock

When the layer is lock, objects is visible but cannot edit
Objects on the locked layer are dim, and a lock icon appear when cursor hover

If you want the objects to be seen, but not accidentally to edit, lock it
You can lock the current layer