If you are talking about why would someone nit pick paying .0003 verses .0004 or .0005. It seems silly when you compare .0003 verses a sell target of .40 doesn't it?
Well maybe not. Look at the math of a fixed amount to invest.
Lets use your $500 as the original investment.
$500 / .0003 = 1,666,666 shares
$500 / .0005 = 1,000,000 shares
That is a delta of 666,666 shares x $.40 = $266,666
That little .0002 difference could cost you $266,666 dollars in profit. So although .0002 seems indignificant is really is huge. This is why pennystock investing is so alluring.
For a $500 investment you could make well over $266,000 dollars. Imagine if you invested $2000 or $10000. That .0002 can make a very very big difference.