Besides preventing one-party domination, what else does the two-party system provide?

They provide the people electing a choice to choose what principles they want the government to lay their foundations upon.

A two-party system is a party arrangement where two significant political fractions command the administrative aspect. In such form of administration, one of the two parties contains a majority in the government and is ordinarily attributed to as the majority or supervising faction while the other is the minority or opposition body. Besides preventing one-party domination, the two-party system provides;

Security: Two-party systems are more enduring and stable than one party or multiparty systems.

Fairness: The two parties must advance to the center to accomplish votes, so the political bodies tend to be conservative.

Efficiency: Voters have simply to select among two parties.