Question

Does it really help pressing the A button many times when you try to catch a pokemon ?

Answer 1

No. The only things that will effect the Catch Rate are the kind of the Poke Ball, the amount of HP the pokemon have, or a status effect such as Sleep, Poison...

Answer 2

Actually not, it's just a Placebo effect

this is the formula
http://archives.bulbagarden.net/media/upload/2/20/Catch_formula_1.png

POKEMON IS SERIUS BUSINESS