I have found this post from Ask the Judges Tumblr account regarding the reasons why pile shuffling your deck is not the best practice to randomize the cards. I myself do this shuffle ritual on every game of my matches from FNM to big events like a Grand Prix. The author describes that the issue that results from this practice calls for slow play and cheating.
Quoting from the article, here are the reasons why:
There are generally three reasons people give for pile shuffling:
1. To prevent “clumping,” meaning when cards of the same type, generally lands, end up in long sequences after shuffling, resulting in a game loss due to mana flood or screw.2. To prevent “clumping,” meaning when sleeved cards physically stick together, resulting in cards of the same type, generally lands, ending up in long sequences after shuffling, resulting in a game loss due to mana flood or screw.
3. To count the cards in your deck, to avoid a game loss due to preventing an illegal deck.
None of these is a valid reason to pile shuffle. Here’s why:
1. This one is straight cheating. If pile shuffling has any influence on the final configuration of your deck, then you did not sufficiently randomize your deck, in which case you are cheating. A genuinely randomized deck is not the same thing as a well-mixed deck. People generally expect random sequences to have fewer long strings of the same kind of thing than they actually do. If I asked you to go flip a coin 100 times and tell me the result, and you lazily just made up the result, you probably wouldn’t give me a sequence with very many long sequences of consecutive heads or consecutive tails. Such a sequence has about an 80% chance of having a string of 6 or more consecutive heads or tails, though the one you give me probably doesn’t have one. Similarly, If I told you to stack a magic deck in a “random” way, you probably wouldn’t get mana flooded. This is why people who aren’t very diligent about shuffling criticize the shuffling algorithm on Magic Online – they get mana screwed more frequently online than in real life, because Magic Online produces something much more like a random deck configuration than your shuffling does.
2. This one is remarkable to me. If you actually have cards that stick together you need to either a) buy better sleeves; b) buy new sleeves; or c) wash you damn hands. You certainly aren’t using sleeves that are sufficient for play at competitive REL. If you mash shuffle properly and they still stick together, stop gluing your sleeves together.
3. This one is the most defensible, if you haven’t thought it through. As I mentioned before, if you shuffle sufficiently after pile shuffling, then your deck should be truly random, so it seems that there’s no harm in it. The reason it annoys me when people pile shuffle is it takes a goddamn lifetime. Slow play is already rampant in magic, especially in paper. The extra time spent shuffling compounds the problem that a slow opponent will cause a draw in paper, in stead of just timing out on magic online. If you are actually worried about having the wrong number of cards, count your cards the normal way, with them facing you. It’s faster than pile shuffling, and you’re going to do it anyway if you have the wrong number of cards.