One of the indirect effects of the 17th amendment was that states always had two Senators. Before it states were sometimes left without a Senator because their state houses couldn’t agree. If the state Senate was Republican and the state House was Democratic, they might never agree on a national Senator and the office was sometimes vacant for years.
Another effect was less corruption, but more populism. Crooked deals were often done in the state legislatures to select Senators. After the 17th passed those deals were unlikely (although party corruption might still happen), but unqualified candidates with a popular message might be elected.
