I guess if you like the cab sims out of the MP-2 or Classic then yeah, good way to stay compact an not break the back.
Few Factors though:
1: The PA has to be decent enough, good speakers and some good decent subs (not always needed).
2: Stage monitor so that you can here yourself, or in ear monitors.
3: Knowing how to mix and getting good quality sound into the front end and stage monitors.
4: some good quality monitors as well, you want some decent tone to listen to.
5: If the stage mix is at a good enough volume that captures the experience, good to go.
Optional 6: If your playing is good you can impress that way (small rack), if not, then I recommend bringing a huge Marshall stack for show...lol
I understand why people downsize all the time and why they would want to get an AXE FX and so on, but really, just stick to the tone you like few different variations, and some nice cleans you enjoy, and good to go.
Even if you listen to some cover bands, the guys are not out to get the exact tone of the original band, unless you are a band like The Pink Floyd experience and so on, then really, what it the poin tin having 1000 different presets...lol
I find I only use maybe 6 different heavy tones, 2 or 3 crunch sounds, and a couple of different cleans with some effects added. The tones I use are not really copy's of anyone else's tone, even though they may sound similar, but I just play around with what sounds I enjoy and go from there.
I'm going to try MP-2 cab sims out into PA as well and see how the goes will play around a bit.
Never though of going direct, but will miss my 4x12 on stage, but not the back breaking hauling though...lol