what are the advantages of lock up and non lock up

locking torque converters ?

locking units allow for greater fuel economy and (if i remember correctly) longer transmission life due to reduced heat from the fluid not having to transmit the power thru the torque converter

The ability to lock up the converter can also improve your acceleration. My car is 2 tenths and 3 mph quicker in the quarter if I lock the converter in 3rd gear.

Some trannys (like some TH350s, THM200C and Ford's E40D and AOD) have some reliability issues with lockup TCs. The GM offerings sometimes stick in the lockup position. Sometimes you'll slow down to turn on a street and when you accelerate again you'll find yourself in third gear with the TC locked up at about 500 rpms Ford's lockup TCs develop clutch chatter very early in some situations. Its more annoying than dangerous, but the vibes can wreck the front pump, seals, and shorten the life of the tranny.

Obvious Pros to a lockup TC are better mileage, less tranny heat, and less power wasted maintaining cruise speeds.