Hi Tony

WORKSTATION
Have great sounds, massive editing facilities, but no pre-set content (Songbooks etc.) so you pretty much have to create what you want from scratch, thus an initial heavy workload. (Chord recognition and programming does come as standard in most boards these days though)

ARRANGER
Is full of easy play features (They were after all originally designed the home market) and are great for knocking up something quick, however very limited when you want to customise.

A combination of the 2 boards (T4 and Kronos for instance) gives you the best of both worlds.

ALTERNATIVES
Add a computer and software to an arranger, as this make even hardware workstations look limited; however the downside is that it requires a good midi implementation on the arranger to get the best out of it. (Not forgetting an initial steep learning curve)

Hope this helps

Bill