So in short, political parties reduce transaction costs of political participation by narrowing the information asymmetry and lowering barriers of entry for candidates to political office, and those benefits are particularly valuable to those for whose such transaction costs are relatively high (i.e. anyone but the very wealthy).
Makes perfect sense to me and is consistent with institutional model of collective behavior, of which I am a big fan.
However, that position can be effectively counter-argued that if the political party system is subverted by the monied interests, not only does it cease to play the transaction costs reduction role, but add transaction costs of its own. For example, if the Democratic party has been subverted, as many claim, by the corporate interests, it will no longer serve as a platform promoting progressive candidates - so its transaction cost reduction function for the progressives is no longer there. What is more, it may use the party resources to eliminate such candidates from running, as some sat the DLC does, and that adds a new transaction costs for progressive candidates, who are forced to battle not just the Repugs, but the Democratic party establishment.
This is not necessarily an argument against party politics in general - but certainly against the party politics US-style, here and now.
Wojtek