Mr Politician... Are you paying.?

The country presumably implements one man one post. Similarly in my understanding one legislator or MP  can represent only one constituency. Someone pl tell me why do politicians stand for more than one seat at same elections? Afraid they will lose? If they win both, they end up giving up one of the seats and a reelection is held at cost of public money. Is the politician willing to pay for it from personal pocket and is the politician willing to compensate every voter for the time lost and the trouble of re-election? Among other things our national and state leaders can do a better job at least in choosing the right area they want to represent at executive bodies. Seems it has turned out to be school admissions.