Discussion Forum

Giving an example deck would be helpful, as one could discuss numbers and strategy's and try to figure out what and why someone used the card x-times.

I can only answer this for myself, giving a general answer will be very hard, as each person builds deck differently...that is if you build decks yourself and don't copy&paste them. The main reason for me most of the time is versatility.

For example my pauper monoW Lifegain Deck
1 Icatian Crier vs 3 Battle Screech
I use 1 Icatian Crier and 3 Battle Screech. Battle Screech has flashback, so I don't need 4 of them in the deck, while Icatian Crier is a strong card that can convert unwanted cards (lands) into tokens, on matches that take longer. I never want to draw Icatian Crier on start, I don't even want to draw it on each game, because Battle Screech is the main card I want to use to produce tokens. If the Battle Screech wouldn't have flashback, I probably would have used it 4 times, and didn't add Icatian Crier.

2 Oblivion Ring vs 4 Recumbent Bliss (with 1 additional Oblivion Ring in the sideboard)
The split here results from Oblivion Ring being more versatile, while Recumbent Bliss can slowly damage your opponent. Even if I would use Journey to Nowhere or Swords to Plowshares, I still would try to squeeze 1-2 Oblivion Ring into the mainboard, because I can get rid of enchantments and artifacts with the Ring, something the others can't. It simply provides me with an option against non-land cards in the mainboard and it isn't a dead card.

From my Rakdos vampire deck
2 Curse of Stalked Prey vs 1 Stensia Masquerade
I only want to have one instance of Curse of Stalked Prey on the field, because I feel that everything else is an overkill, so I went with 3 Curse of Stalked Prey in the beginning. When Stensia Masquerade came out I did replace one instance of Curse of Stalked Prey with it, because the Stromkirk Captain's in the deck tend to get killed rather fast (or as fast as possible, if you ask some of my opponents ;) ) but first strike is necessary in this deck.

2 Read the Bones vs 2 Sign in Blood
Sign in Blood is cheaper and faster, but it "only" allows your to draw two cards and need {B}{B} to cast. Read the Bones on the other hand costs 3 mana, {2}{B}, so it's easier to cast and it allows you to scry 2 before you draw 2 cards. The advantage of Sign in Blood is that its cheaper and thus faster, while Read the Bones has advantages in easier colour-requirements and being stronger in games that take a little bit more time.

From my wifes MonoG Wolf Ramp
1 Garruk Wildspeaker vs 1 Garruk, Caller of Beasts
Now here you have a complete different reason to split cards. This is my wifes deck, and I supported her with some cards, others she did buy at our local gaming store, but in the end, she decided to use those two planeswalkers, because she already had them as real cards, they where a great addition to the deck, but the deck could run very well without them. If you draw one of them it's fine, if you don't it's also OK.

2 Inkmoth Nexus vs 2 Kessig Wolf Run
The deck uses Primeval Titan to search for special lands and then pump up Inkmoth Nexus or any other creature you want to. I we didn't want to rely on 1 copy of those special lands (and mountains) so we added 2 of them in the case one somehow got destroyed. If you're up against land destruction, this deck will have to rely on other means to win, because getting rid of 4 special lands is a no-brainer for LD, but other deck usually only have LD in the sideboard (if at all) and normally not enough to pose a real danger to all of those lands.

Last, I wrote a description on how to build decks, a long time ago. One of the points was "Play cards 4 times!":
You have a strategy and you have some cards that you want to draw to win this game, those cards are key-elements to your plan. So if your deck and strategy is built around certain keycards you can question yourself “how often do I want to have those in my hand or on the battlefield?”. The answer in most of the cases will be “as often as possible” so have as many of those in your deck as possible: 4 times. If it is part of your strategy to have e.g. a counterspell on your hand in turn 2, you should not just play one type of this spells 4 times but two or even more.
Cards that you don’t want to have on your opening hand, can be reduced to 2-3 copies. This ensures that you have a chance of drawing them later on when you need them. The same goes for legendary cards because you normally don’t want to have more than one on the battlefield and perhaps a second one on your hand. If you have a high number of spells that let you draw cards, or you're using cards that let you search for other cards (so called "tutors"), you can reduce those numbers to 1-3.
It’s also pretty hard to judge a deck that consists of an extreme amount of different cards. Most times one of the first comments you will hear (at least from me), if you don’t follow this rule or explain why you don’t follow it, is that you should play important cards 4 times.