I'm searching the net for tilesets and sometimes i would stumble into a tileset that looks like this - http://opengameart.org/sites/default/files/grassland_tiles.png

what i don't understand is why are some images/tiles here are cut in half, and some are whole. Check row 4/5 fences or check the boats further down.

Now scroll a little more down and see some of the larger images are whole but the house are cut in pieces.

Seems like a question you would want to ask of the tileset creator.

It fits more easily into the tileset that way. Observe:

In tilesets (spread out to grab rectangles of pixels):



In games (rectangles of pixels overlapping):



[size=2](Pardon my uneven red lines that don't properly line up)

How are you going to separate the tiles properly, if the middle chunk actually goes one row lower (one half-tile lower) than the others?
The chunks of the house on the left and the right are half-obscured by the center chunk of the house.

Remember with isometric tiles, every other row is offset by half a tile both vertically and horizontally. So if two pieces of tile fit together on two seperate rows, the one tile behind the other tile will be half obscured.