You might not think it was a big deal, but getting the chips to fall (reliably) out of harms way is the biggest plus I can see for a slant bed. A conventional bed seems to have more places to snag and pile chips up.
Also, I guess that it is easier to see what is happening in the cut zone on a slant bed, and when doing tool setting, without having to lean way over, and so on.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)