Absolutely not. Here are my reasons:
1: It lowers the clearance underneath the table, which makes me sit lower and prevents me from crossing my legs or sitting higher up. It also makes the table top feel too high
2: It put me further away from the desk, so I cant reach things as easily on the table as easy and directly left or right of hands is air rather than more desk space. If the keyboard was on the desk, i can have things between the keyboard and my body and everything is left, right or further away is still more within reach
3: I cant rest my arms on the desk when i type so I either have to perch them on the chair arm rests, which not all work stations have, or just have them hanging in the air, which sucks.
4: It either a) limits the amount of mouse space you have to a tiny square or b) makes you put the mouse on the desk, at a different height and depth.
5: When you actually have to use the desk to write something, you have to push the whole tray in to scoot up and use the desktop then scoot back out and pull the tray out to type again.
Overall, other than that you can shove teh tray under and hide it to make your table look more clean, I cant think of a single reason why I would get a desk w/ a keyboard tray. My current table is ideal. It's wide and it's deep so I can have the monitors at a resonable distance while still having plenty of space for a keyboard and work space on the desk