I had a dodgy MOT on a vehicle a few years ago, I knew it wouldnt pass on a few things but they were all more or less minor bits. But, I did trailer the vehicle there so it could be checked to make sure it was safe, I got a handwritten defect sheet so I knew exactly what was wrong with the car so I could rectify it later.

The reasoning behind getting one was that I was unemployed at the time and the car was still taxed and insured but had ran out of MOT - I had a job coming up but needed a vehicle to get me there hence why I got one, I did have the vehicle repaired on my 1st payday and taken back to the MOT centre for a clean bill of health afterwards.

There are those that will get bent MOTs for anything thats below scrap quality but there can be some genuine reasons behind getting them, such has what some people have already mentioned ie emissions, decats, etc etc

Jut my 2p's worth anyway.....