Every once in a while someone will ask the question "should I be playing ranked matchmaking?". I would like to posit my opinions on the purpose of separating ranked and unranked play, and also provide some questions to ask yourself to see if you would be better off playing in the ranked or unranked pools.
The Difference Between Ranked and Unranked
Dota 2 matchmaking uses a rating system to try to arranges balanced matches contain players of roughly equal skill. The matchmaking rating, or MMR, that a player is assigned is based on how they perform in games, with wins awarding additional rating, and losses removing rating points. Both ranked and unranked matchmaking pools assign different ratings to the player. They are functionally identical, except that a player's ranked MMR is shown, and their unranked MMR is hidden.
Why Separate Matchmaking Pools Exists
So if the MMR for each pool is identical, why do they make two separate pools? The answer is that some players want to know how they compare to others. Some players want to be the best, to improve, to win games. The ranked MMR serves as a metric for a player to identify their skill level, to track changes in that level, and to push their rating as high as possible for personal satisfaction and to indicate their potential to others.
Differences in Player Motivation
Dota is a competitive game. Like any other competitive game, every player plays the game for different reasons. Generally however, most players play Dota because they want to have fun. The problem is that different players will have fun by playing the game in different ways, and sometimes the different ways that players like to play the game are not compatible.
Everyone can agree that winning is more desirable than losing. However, there are often situations in which a player is faced with a decision that presents a trade-off between maximizing your own personal enjoyment of the game, and maximising your team's chances to win the match.
As an example, imagine you are in the pick stage, and your teammates have already picked three core heroes. You were hoping when you queued for the game to play your favorite hero, Anti-mage, however, you know that if you were to choose AM now, your team would be heavily disadvantaged due to a lack of heroes who do not depend on items to perform. In this situation, you have to choose between playing your favorite hero and having more fun in the game, or choosing a hero you enjoy playing less in order to improve your team's chances of winning the game.
I believe that the decision that a player makes when faced with choices like this is a strong indication of what matchmaking pool they should be queueing for. It is not wrong to make a choice that maximizes your personal enjoyment of the game. However, the purpose of separating the pools is to allow players who prefer to maximize personal enjoyment over winning to not be placed in a match with players who will always choose the option that maximizes their chances of winning.
What Matchmaking Pool Should I Be Playing in?
In order to determine which pool is the best one for you to queue in, you should first ask yourself some hypothetical questions.
Most importantly, when faced with a decision, will you always choose the option that you believe maximizes your team's chance to win the match? This question can be applied to every decision that a player makes in a Dota match; from the choice of hero, to the choice of starting items, lane, ability build, item build, choosing to watch the minimap, making choices about when to farm, when to push, when to fight, when to rosh, when to retreat, how you choose to interact with your teammates, etc.
This question is also relevant to factors outside the game. Do you actively pursue outside guides, learn mechanics, or read discussion, in order to improve your play? Do you own a microphone that you can use for voice chat? Is your internet connection poor right now? Are you queuing with friends who are not as good at the game as you are? Are you distracted by outside things like people or pets? Are you taking intoxicants that will lower your effectiveness? All of these are decisions that you can make which have an effect on your chance to win Dota matches, and if you are not making the choice that maximizes your chances of winning, then perhaps unranked would be a better fit.
At the end of the day however, no one can decide which pool you play in except for you. Keep in mind though that ranked games attract players who have a stronger desire to win, and if you don't share that desire, and actively pursue victory over your own personal enjoyment of the game, there will often be friction between you and your teammates. Unranked matchmaking is the place for people who just want to have fun and enjoy the game.