I would not use the word needed.
Its More of a choice.
they used to say they ran hot,
I never had a problem with that.
they also would say you would lose mph with a spragless converter.
I never saw that either,I ran and run a Big Block.
Everybody bad mouthed the spragless converters until the patent ran out.
ATI even used to place ads in national dragster about how bad they were but now ATI offers spragless.
When the patent ran out now all the big company's offer you a choice of sprag or spragless.
ATI,Hughes,Coan, For a fact they all offer it.
I ran one back in the 80s and run one now.
they also used to say if you want to go fast you need a sprag,
I was told by many different companys that the spragless technology has come a long way.that today there is no difference.
IN my new car they asked me which i wanted and I choose spragless,to me its just one less thing to break.
years ago after maybe 500 or more runs on one i did flatten the fins in a converter but didnt hurt the sprag because there was none to hurt.
I ran 7.80s with one @ 175 on all motor.
they are also very consistant.
I have always run Trans Specialities,they are local ,close and never had a problem with anything they have ever done for me.
All Throttle,NO BOTTLE