It is often believed by beginners that double pawns are bad, but this is far from the truth. Rather than adopt a simplistic view one should study when doubled pawns are favourable and unfavourable. Here are few typical situations in which the strength or weakness of doubled pawns is worth noting:
1. Doubled pawns on an open file can become a serious liability and will be difficult to handle.
2. Doubled pawns in endgames came out as serious weakness if they are a part of pawn majority as they can render that majority unable to produce passed pawn. In this case the your opponent has a virtual material advantage.
3. Doubled pawns in the center are often more useful than doubled pawns on the wings because the offer extra central control.
4. Doubled pawns offers an extra half open file to its owner which should be evaluated thoroughly.
5. Isolated doubled pawns are more weak than doubled pawns in chain.
6. Sometimes kingside doubled pawns are very useful in launching an attack against the opponent’s king. An example of this can be found in the Tartakower-Korchnoi Variation of the Caro-Kann, which goes 1.e4 c6 2.d4 d5 3.Nc3 dxe4 4.Nxe4 Nf6 5.Nxf6+ exf6. Black can often use the pawn on f6 as a battering ram with …f6-f5-f4-f3. Meanwhile his king will be safe because he still has the pawn on f7.
7. I have learned through experience that doubled pawns can be more disadvantageous in relation to pawn islands. The more pawn islands there are the weaker the double pawns.
Any more general observations in relation to doubled pawns are welcome here if you comment on this post.