Ghost stations can be used in play quite freely and are difficult to block, although there is rarely any need to. Their coefficients are much lower than they would be if they were still in use and tokens placed on them may not always have the usual (or indeed any) effect.
Skilled players are able to use some of the weaker ghost stations as a close equivalent to a farkle, when other rules specifically prevent this action.
A list of ghost stations is available.
[TCM]
Strictly speaking, when dealing with ghost stations, any move should be referred to as a glime. In practice only purists and pedants feel the need to take the game to this level of detail.
[SM]