Bathtub installation and Mortar

Purchased whirlpool tub. Is NOT a drop in. Says I am to mortar the floor that it will sit upon when I install. I understand need for that IF it was just a tub.. However, this tub came "mounted" on a wooden board. I don't see how mortaring under the wooden board will benefit the tub in any way.. .Is this board to be removed upon installation? Any info is greatly appreciated.
Thx.

the mortar is to level and support the tub. plywood stays. usually the bands holding the pump get cut. check your directions.

Directions just said to put down mortar under tub... Still seems crazy to put down mortar then the board and tub on top... I can see how it will allow you to level the tub, but don't see how it "supports" if a very heavy person were to stand on one foot in middle of tub.. Would seem to me, that if you mortared between tub and board, you would be able to have support under the whole tub, and the chance of someone "cracking" it would be reduced.
That all being said, the mortar goes between the floor and the board CORRECT? So far as I can tell, there is nothing between the tub and the board it is attached to except that the tub touches the board in some places.
thx again for any help.

Many tubs come with a board under them.

If you use mortar, or fixall, or plaster, it would be under the tub with board.
Not between the tub and attached board.

tub

If the board sets the tub level and you are going to build the platform up to the tub rim, then the mortar is not necessary, and would only raise the tub higher.