yeap have seen the above such cases too.
Have even tried it. 
Imho , its not very good technique , bench press supposed to train
the chest ,
however , using the above technique as well as the variation of
legs bent above the bench , some of the abodominal muscles can be
put into play to lift the weight.
I suppose its good at the end of the set when your unable to even
lift the weight off the chest with conventional means , then to
push yourself harder you use this technique i guess
