It's most important function is as a tool of strategy. Once you have mapped the environment then you can start to ask yourself questions of where you should change the landscape. Do I want to industrialise this component or protect this space? Mapping simply provides you a view of the chessboard, you now have to do the hard work and start by identifying where you can move (see figure 1).
Figure 1 - Where with Maps
Once you have determined the possible wheres then you can determine the why of strategy as why is simply a relative statement of why here over there. That choice of why should be determined by numerous factors from suitability, ability of competitors to play the game, opportunity to create ecosystems and take advantage of componentisation & volume effects, inertia, resource constraints, your own desires (see Nilan P's point below in the comments) etc.
Once you have your why then you can determine the how - use of an open approach to manipulate the environment by encouraging commoditisation, introduction of a tower and moat play, creation of legislative barriers etc. There's a long list of games and dark arts that can be played. Once you've determined this, then you can determine the what and when of action.
Mapping is far from a perfect representation of the environment, in fact perfect representations are never possible. It is however generally useful in the same way that looking at a chess board is generally useful when playing the game. Mapping won't make you a great chess player though but it should give you an edge over those who don't look at the board.
As for how many don't look at the board in the game of chess they're playing ... it's surprisingly common. To find out if you're in this camp then go grab you're IT or Business strategy, whichever is closer. Rip out of the document any references to purchasing choices, implementation details, operational details and tactical plays and leave only that which refers to the "why" you're doing whatever it is you're doing.
If that "why" is vague, often hand waving with generic platitudes such as "innovation" and "opening new markets" and you have a sneaky feeling that the real why often appears to be because everyone else is doing it (e.g." 67% of successful companies are doing cloud and so should we") then you can safely bet that no-one is looking at the chess board.
However, don't fret if your company is running blind. The chances are your competitors are as well and really that's all that matters, relative positioning ... until of course someone else enters your market.