Chalk another vote up for the IR2135TImax
I have one and wouldnt be without it.
You asked the question "what can a 3/4" do that a 1/2" wont do"
Well that is a hard question to answer because they are all different.
The 1/2" can be had from a low as 100ft-lbs to 1000ft-lbs
The 3/4" can be had from ~600ft-lbs to over 1500ft-lbs
So I guess if you have a 1/2" with 1000ft-lbs and a 3/4 with 600, the 1/2" can actually do more.
And as far as sockets sizes go, I personall have a 1/2" set AND a 3/4 in set And use adapters for the 3/4. My 3/4 set is 7/8 up to 2-1/2 and my 1/2" set goes up to 1-5/16.
So I guess to sum it up, for a home shop (unless you are a trucker or big farmer) get a 1/2". They are a lot lighter, they are faster (3/4" are SLOOWW), and even the good ones are usually cheaper.
And DONT get the $30 ones at walmart or a-zone. I have had a few of them and its a 50/50 shot as to wether they will even break a lug-nut on a car loose:confused2: There have only been a few times my 2135 has let me down. And both times required the use of a 24" pipe wrench and a 4' bar as still a lot of grunt.
If you have a big tractor or equipment a 3/4 might be nice. I have a 3/4 socket set but only use it once in a blue moon on the equipment I have.