Sorry I know this is random, but that word just brought up my friend. He think the word for being able to write, etc. with both hands is "optimistic".
I guess it would fit for Optimus to be Optimustic.
Sorry for the bad pun.

 

Sentinel took his right hand man, then he took his right arm.

Because it didn't happen on screen, everyone always forgets on thing.
Allow me to elaborate:

Bumblebee has legs now.

 

You owe me a new desk. Because I just hit it so hard with my head.

 

"Why he need his right arm?" to be in a normal condition that's why.

Optimus was literally disarmed, but he could still put up a beating as a handicap. I would be surpirsed if he doesn't need his arm, when he can be fixed by Ratchet.

 

If I were left handed, I still think I'd quite like to have my right arm still be attached.

 

Everybody gets lucky once.

 

Okay, now you owe me a desk.

 

Only Decepticons are left handed!  

 

"Better...stronger...faster..."

*cue theme music*

 

Thank you.

 

He could also simply reattach it like Starscream did. I don't think it is very difficult to repair an arm or limb. Except if you are Megatron and the damage is too catastrophic to be fixed.

 

I have to say it;

Prime is right-handed.

If you pay attention, (or just happen to notice after much deliberation on platypi,) whenever Prime uses a weapon, he uses his right-hand first. Take, for example, the first movie (or any shot from the trilogy with his ion cannon). Prime only uses his right ion cannon. Another example is the warehouse scene from ROTF. When Prime breaks in, the barrage cannon (-the guns of which he has two copies,) he bursts in holding is held in his right hand, before he jumps over Megatron and pulls out his other one. Then there are his swords. The first time he uses a sword, Prime transforms his right arm. We only learn he has a sword on his left arm right before he says "I'll take you all on!" In DOTM, the sword he holds is in his right hand. And, finally, in DOTM, when he walks into Chicago for the first time, his trigger-finger is on his right hand. In other words, he's holding the gun primarily in his right hand. So yes, he kinda needs it.

And now that I have brought new information,

 

But, then again, I guess someone had to ask.

 

people are getting to into this its simple optimus prime is as micheal bay says he is

 

~*~lik dis if ur a strng betiful autobut~*~
~who don't need no arm~​

I dunno, I think it's just better design to have more than one arm. Two legs, so symmetry would be nice.

 

Yes I would have to agree but Optimus[like myself] can use both arms with dexterity.

 

I had that in my sig a while ago! Thief! Lol Jk with you bro.

 

Da fuk?

Sure he may not "need" it but it sure as well will be better to have both arms. How about you cut off your own arm then learn to use the other? You don't really "need" both arms.

 

So...the harbringer of death.

 

Yeah, I saw it in a signature a while back, I just wanted to quote it XD