For a starter of why having a cracked account is bad is that you cant join servers that don't have online-mode set to false, And you can't change your skin easily. And most popular servers are not cracked so Cracked Players can't join. One more bad reason to have a cracked account is that you cant view your skin in a skin viewer that ask for the players username, Because you don't have your skin uploaded to the Minecraft database that the skin viewer gets the skin from.
Now a one good reasons to have a cracked account(There are probably more but this is the only one i could think of.):
You did not have to pay for the game.
So the main thing this blog is saying is its better to buy the game then to crack it, Because you get more features. And dont try to get a free Premium account, Because most websites that say they give you a premium account just give you a virus.