I can provide you with the reasons why I went for a vasectomy but from speaking to other men, the motives can be very wide ranging.
Anyhow, as far as my wife and I were concerned, she had already had two girls from a previous marriage. at the time we married, the girls were aged ten and five respectively. Now athough there was a history of post-partum haemorrhage in her family, both girls were delivered OK.
When she became pregnant with our son, the pregnancy and birth went like a dream with no problems. Shortly afterwards we decided that three children was enough and neither of us wanted more. As a result, she put her name forward for sterilisation.
The sterilisation op seemed to have gone OK and the clip method was used for securing closed both her fallopian tubes. Around six months later, she began to have unexplainable body pains similar to flu and felt very out of sorts. A GP told her he thought it was virus. Something made my wife suspect that she might be pregnant and she did a home pregnancy test. The result was positive - the GP has never lived it down.
The pregnancy itself went OK, but my wife haemmorrhaged post partum severely and almost died. Her entire blood volume was transfused three times, which I think is about 24 pints and she was at death's door for almost a week drifting in and out of consciousness. It frightened the hell out of me but she did slowly recover over a period of three months.
Following investigations almost a year later, it turned out that the gynaecologist who performed the sterilisation had not secured one of the clips properly on one fallopian tube.