Ever throw away a card you needed - and thought the machine didn't
hold it?
Yes, you can get a "sticky" button, and it rarely benefits you. I
usually move right away if I don't like a machine's performance (I
also don't like "silent" machines because that little noise a normal
machine can make on a dealt paying hand has saved me from accidental
bad discards).
I admit it - I've thrown away that second pair in JOB because I grab
the pair of Jacks or better on the left and hit the draw button too
quickly trying to keep my "hands per minute" average up. Too fast-and
very costly.
Clearly, when you play for comps, time is money, and the more hands
you get in (and more coin in), the better off you are, especially on
double points days, etc. as the payback plus comps can put you over
100%.
Just don't play so fast that you "discard" away your edge.