They make a difference if you're charging down narrow twisty single track through the woods! Very handy for snagging on branches, foliage, and my favourite... brambles :facepalm:
They seem to suit 1990's MTB'S With flat bars and long, low stems, useful for extra hand positions on long rides, and I find they give me a more natural riding position on long climbs, similar to riding on drop handlebars.
However, riding my modern bike with riser bars & shorter stem, I don't miss them one bit. I've ridden further, and longer, on my modern bike and found that I can live without the extra hand position, and have no need for them on the climbs.
These days, I think bar ends are more suited to touring bikes, town bikes, or those retro Mtb's from the 90's.