Over the years, some players invent (or discover, if you prefer) a particular move, which they use for a specific purpose.
When it works well, other players adopt it into their games.
Note: The diagrams here are just examples and should not be followed blindly - the exact position in actual games will vary quite a bit and must be taken into consideration when contemplating use of these moves.
Teta I5:First used by the great player Teta quite a few years ago (2006 or 2007 perhaps?), this move consists of cutting off an area of the board but playing the I5 perpendicular to, and reaching, an edge of the board.
However, it must be used carefully, because, in addition to cutting off an opponent's color, it can also cut off its own color!
Also, if the opponent's other color can reach that location, it can work out poorly. By contrast, if the PLAYER's other color can get there, it can bring home a bundle of points.
More info at IWK's Strategy Blog
The Guiduf I5
The Guiduf I5, by contrast, is an offensive move used early in the game.
Used as the third red move in certain situations, this risky move is designed to advance red
quickly past green to upper left part of the board.
In order to determine whether it should be used, a player must carefully consider what Yellow and Green can or will do.
If Red can play N on his next turn to advance to the upper left, leaving green behind, it will turn out very well. But if Green is in position to cut off the end of the red I5, it will work out rather poorly for Blue/Red.
As with so many things in this game,
"it depends ...".
Pioneered by Mike Yosuke in Freestyle games, this is also a very specific move.
The fourth blue move is the Y piece, which sets up a very strong defensive position, while still advancing blue towards the center of the board.
This move, used often by Norocgogule, though he may not have been the first, also fulfills a specific purpose.
The Blue X is played with the idea of making Green's life very difficult, and often leads to a very low Green score.
[ Editor's opinion: Green kill, while sometimes very effective, is a strategy leading to a not-very-fun game. ]