Work limbs seperately?

[udo]

Does it really make a difference if you do exercises for both sides of your body or a single one(i.e. bench with a bar vs. dumbells or dumbell vs barbell curls)?

No real reason, I'm just curious.

[Ronin]

Lets take the Bench press:
You do it with a machine you can use alot of weight
You use a barbell, you will use less weight because you will need to stabalize the bar and your stabalizer muscles are the weakest.
If you use dumbells, you will use even less weight for the same reason, but you will need to not only stablize more , but , your weight will be restricted to the amount your "weaker" arm can use.

[udo]

So are you saying that one is better than the other or just outlining the differences?

[Ronin]

Just the differences.
Wither one is better than the other, depends on what you want.
Personally, I don't do an dumbell work, But I am thinking of changing my overhead press from barbell to dumbell, I think my left shoulder is holding back my right and with dumbells, you can see if that is for sure.

[Nid]

Part of the value of full range reps is the flexibility aspect...that's why I like dumbells; yaren't quite so pigeon holed. However, I like increasing weight in teeny tiney increments. Dumbells aren't so good for that...at least not the ones at my disposal.

Conclusion: personal preference.

[The Wastrel]

keinhaar hits it on the head. I like dumbs because I like to train the weakest part of the motion. The bar is lowered from a strong position, dumbs have to be lifted from a very weak point. I will only lift dumb weights that I can lift through the whole motion.

[Djimbe]

I prefer dumbells for the Reason that Ronin mentioned .

Your Stabilisers cant be worked enough as far as Im concerned , Especially as A Martial Artist . for better results in the Martial Arts , I use Dumbells at every Possible (read : Safe) Opportunity .