Sorry if this post comes off as a bit scattered.... that is because it is. I posted it anyways, hoping to spark some discussion.
The metrics and details that the deck builder in DeckStats.net is a huge benefit that is offered here over other websites.
The math and details behind this tool can be a huge asset to tuning and optimizing your decks.
I find that I only really use those features on decks that I am tuning for competition, but some of what the probability section offers can easily help you while planning and designing a deck as well.
There are certain standards and numbers that folks use while building decks. 40% land is a good example of that. The next land thought is making sure your colored mana mix supports the mana requirements of your chosen spells. The details tab has some nice Pie charts to help show that ratio.
One of the less obvious uses of the probability measures is the ability to determine probability of a TYPE of spell showing up, not just the cards or land/mana colors.
A control deck designed to use Blue and Black functionality to control the early to mid game of your opponent would normally contain counter spells and removal. How many counters do I need to play to normally see 2 of them by turn 4 or 5?? Nine of them will give you a more than 50% chance to have that happen. How much removal to see 3 in the same amount of time?? You would have to have Fifteen of them for that.
This is a fairly simple example of how to use that chart to help design a deck.
It is one thing to take advantage of these numbers while building, but what about playing??
The ability to remember the numbers is a skill that many pros and strong competitors can do.
It is not usually allowed to have your Deckstats app up on your tablet to access your info while playing, but you can have some notes.....
I have built a grid that I can print off, that displays some of the generic numbers that the probability charts give on the deck page. I have the columns listed 1 through 12 on the Y axis, and Hand and the first 5 turns on the rows
X axis. The grid gives me the percentages of seeing the card based on how many in your deck... up to 12 for the first 5 turns, and I can reference it on the fly. This info can now help inform some decisions, like whether or not I should counter this creature now..... or remove it later. Am I due for another counter spell soon??
I have also set this up for Brawl and EDH.... obviously not useful for specific cards, but it works great for land and Types of cards.... and still provides good information to help decide which direction your plan should go.