I use both. Same identical sound if you use the same settings. amp and cab = amp block + cab block.
I figured out that I can run a compressor between the amp and cab, and I do that sometimes. So that's the only time I will use 2 separate blocks, when I need to put something in the middle.
The compressor to me is not suitable for every situation. But sometimes it really makes fast playing a lot easier, for all the shreddy solos, or really fast aggressive palm muting. It also makes clean solos sound like they are supposed to--compressed, bold, not whimpy. When placing the compressor there, I always turn down the ripple of my amp, otherwise there's a low frequency hum that appears.
However at the same time the compressor adds a certain amount of "harshness" and depending on the signal chain can even make my preset develop certain artifacts, such as pops. So I use this trick sparingly.