We are a commune of inquiring, skeptical, politically centrist, capitalist, anglophile, traditionalist New England Yankee humans, humanoids, and animals with many interests beyond and above politics. Each of us has had a high-school education (or GED), but all had ADD so didn't pay attention very well, especially the dogs. Each one of us does "try my best to be just like I am," and none of us enjoys working for others, including for Maggie, from whom we receive neither a nickel nor a dime. Freedom from nags, cranks, government, do-gooders, control-freaks and idiots is all that we ask for.
We consider curls, whether dumbbell or bar, to serve an aesthetic purpose more than functional muscle development. Biceps and brachialis are not highly-functional muscles but, unless over-developed, sturdy ones look good to females. That's why they are Curls for Girls. (Of course, toned arms on women likewise look good to men.)
Vanity of vanities...
The opposing muscle, Triceps, is a much more functional one so if you strengthen triceps you have to balance it with some biceps development.
Following orders, I did a very tough sequence of barbell curls this morning: A sequence of one to ten curls with 7-second rest between. (ie, 1 curl, 7 second rest; 2 curls, 7 second rest, up to 10). Then, after a one minute rest, backwards down from 10 to 1.
After that, picking up a coffee cup is a challenge.
Sorry (not really) to disagree, but people tend to overemphasize the "pushing" muscles and neglect the "pulling" muscles - as well as upper body vs lower body.
I will agree that an argument can be made that people overemphasize the muscles that are seen from the front (which includes biceps vs triceps). However, the gross overemphasis on the "pecs" vs the back muscles results in relative neglect of the biceps.
I'm firmly in the camp that believes one should do twice the amount of pulling than pushing. From a functional (useful) standpoint, curls are not really needed as they get plenty of work doing chin and row variations. That said, from a bodybuilder standpoint, curl variations are needed for looks. I will make the same argument for triceps - they get enough work with pressing movements. There's only so much time and energy to expend and I thinks it's better to work really, really hard on those movements that give me the most bang for the buck rather than "wasting" time/energy on other movements which by necessity detract from my primary exercises.
"Isolation exercises are good if you have a little spare time..."
The problem - as I see it - is that we all have a tendency to fall into the trap of "if a little is good, more is better." Given that there is an optimal amount of work you can do and that below this optimum, the stimulus for improvement is sub maximal, and above this optimum, recovery is impaired, it follows that if you add a few sets of curls, you really need to remove something else. Everybody wants to add the few sets of curls (or whatever), but we are all reluctant - even if we know better - to remove the something else.