The bottom of the tub in my suite has a hollow are where a little bit of water remains after the all the rest has drained away. Over time, the evaporation of this pool results in a stubborn stain on the bottom of the tub.
Wiping it up or into the drain after each use is a pain, but necessary to avoid that build up of scale if you take pride in your tub.
The same problem occurs along the back of the tub lip against the wall. The tub has a curl slightly downwards as it approaches the tiled wall. At least mine does. Wiping the water up after each use again saves a lot of scrubbing later.
Another problem, potentially more serious, is that the front corner at each end of the tub is shaped so that the water lying against the wall is not prevented from slipping over the side of the tub and down the face of the tub against the wall. Over time, this periodic wetting of the baseboard can wreak havoc. A wood or fibreboard baseboard may swell and separate from the wall, allowing a crack which is a haven for mold. Even a tile baseboard needs to be properly caulked to prevent water from collecting behind it.
The water, over time, can cause the metal wall studs and plate to rust, mold to appear on the drywall in the wall cavity, and in severe cases to destroy the baseboard on the other side of the wall.
The remedy is relatively simple, if not elegant. Apply a bead of caulking on the rim of the tub from the corner of the tile diagonally to the where the rim turns down inside the tub. This will trap the water from going over the outside of tub and if there is a lot of water, as in a prolonged shower, will direct the extra back into the tub. You can also buy water dams at the hardware store which you caulk into place at the outer corners of your tub.
Also, check that there is no gap between your baseboard and the wall at the tub. As a precaution, run a bead of caulking along the top of the baseboard and along the top and bottom of the quarter round at the floor, if there is one. The bathroom is a humid place; keeping moisture out of enclosed spaces will eliminate the water damage and discourage the formation of mold.