Some times, while I’m watching some tutorials, they use an “Apply transformations” option.
- Why is this necessary?
- What happens to the object then?
- What its shortcut, and where is it in the menu list?
It multiplies each vertex by the object’s transformation matrix, saves the result in to the object’s mesh data and then resets the matrix.
It’s necessary because while there are many uses for keeping the transforms intact, modifiers and some operators perform operations in object space (and rightly so), making the results often unexpected to users if they weren’t quite paying attention to what transforms are on the object at the time.
It’s under Ctrl-A, or in the Object menu.
Thank for the answer, however it was a little too much technical for me!
Can you explain it in a real life example?
It’s just that Blender is built to try to do everything. And some function and methods overlaps each other.
Ability to animate scale is one of the reason object scaling is there. If you look at key frame options, scale is one of them. Animation is programmed though object level, and not on thousand vertices it may be built up on it. Scaling deals with the whole object without destroying mesh structure with in it. Suppose you want to animate squashing a ball. Then all you do is use Z axis scaling to animate it.
there you got a very technical (thanks Piotr 
and a real blender example )
thing to remember is if it all goes wrong x-(
apply scale/etc then try again
Did I understand well, or this feature is only essential for future animations?
- Should I care about it when modeling or texturing?
- Does it l resets all my model units to 1?
its sets SCALE to 1 (units within the mesh stay as set by you)
it can mess up uv mapping therefore textures can be scaled wrong
it can do funny things to some modifiers
as I said try it IF it all goes wrong back up apply scale then do whatever went wrong again