My experience with them is quite broad, so here's Mr. Nuance for ya.
Gigging with them can work, if you have
a) the right lunchbox amp that doesn't sound small to begin with
b) use 2x12 or 4x12 cabs that add to the perceived heft in sound.
I've gigged occasionally with a H&K Tubemeister 18, Carvin V3M (both sold) and my Engl Ironball (all EL84 power amps), and with 2x12 and 4x12 cabs only.
Yes, they'll struggle to remain clean when working with a loud drummer (which my band's drummer definitely is!) and the drive can sound congested due to the lack of headroom. The upside was less weight and hassle in transit.
Eventually I settled on the in-between option for gigging: 40-60W amps that don't weigh too much (<32lbs/15kg), but still have big glass & iron (6L6 and EL34), combined with a big sounding vertical 2x12" on casters. Portable enough, yet still enough ballz.
To me this is the best compromise for semi-pro musicians that do care about their tone, but also about their back in the long run.
Occasionally on really big stages I'll bring out the Engl Invader and the 4x12 cab.
In the studio lunchbox amps have proven very useful, especially when going direct through the Torpedo Live (IR's), where you can pair them with bigger sounding cabs/IR's and in some cases the 'smaller tone' that takes up less sonic footprint helps with getting leads to stand out more than to have a big sound that takes up most of the mix.
I've had the Engl Ironball used for leads, where I preferred it to bigger amps, but I used the bigger amps for rhythm tones to greater effect.
When it comes to home practice/bedroom-playing, it's 50/50 for me.
The lunchbox amps typically are easier to get a good sound on lower volumes, although I've run into a few that still want a decent amount of volume before they open up and deliver the goods.
On the flip side, if you find a bigger amp with a very good master volume, it may give you more girth in tone and in turn more joy to play it.
Of course, that additional girth in tone may actually be unwanted when you're in a dorm, or a noisy apartment or something, where neighbours will complain sooner because of the droning bass noise.
For now, I've settled on 2 lunchboxes to keep around, where especially the little Mark V:25 would be my desert island bedroom amp, but most of my playing time at home is on the Engl Savage 60 or Mesa DC-5; both 24" heads with 50-60W, EL34 and 6L6, run through a 2x12 cab.
The Ironball I sometimes bring to rehearsals, when there's a 2x12 or 4x12 cab in the room, and I'm not too keen on whatever run-down & abused head I might encounter there (typically JCM900's, H&K Warp 7's and crappier stuff). That way my tone is controlled and I'm not dragging along some 50-60lbs head just for a rehearsal.
YMMV.
