Consuls had the power to veto what the other one did. The Romans hated kings and single ownership of power, so they figured it would make sense to have two at the seat of the executive to put a check on the other. The consuls did have the same powers on paper, but some consuls commanded more respect, especially if they had been consuls many more times than their partner. View it kind of like political capital. A president can't get much done if they do not have the support of the people.

Also, if a consul died and a new one was elected, that new consul would serve out the remainder of the time of the previous consul. The consul that was still in power was considered to be the more influential and more important consul, because he was elected at the beginning of the term.