With Campy Brofters you can sweep the chain across several cogs quite effectiveley.
The advantages of bar-ends are mainly for more adventurous tourists. Originally they were the alternative to downtube shifter for tourists, tandemists and CX riders:
You can build up any transmission system you like, no need to stick to systems.
You can replace any transmission part after damage: field replacements are generally the steel Shimano SIS variety. Rear mechs esp can be damaged by airport handling and minor crashes.
Simple, reliable, rebuildable construction. If your bike ever takes a swim in a muddy puddle, fine grit will enter the shifters.
You can use long-pull drop-bar brake levers to work more effectively with V and cantilever style brakes.

The downsides are the long cable run, the interference at the knees and possible damage to shifters in a slide.