CMV: if you live in an uncompetitive US House District, you should register with the majority party
Less than 10% of US House Districts are true "toss up" districts. Eighty five percent are not competitive.
That means that for most voters, the outcome of the election is decided in the primary, not the general election. For many primaries, you have to be registered with a party to vote in their primary. In fact, if you have to choose one, you're better off just voting in the primary election and not in the general.
Registering with a party, even if you detest everything they stand for, has no downsides. Besides participating in their primaries, you're giving them no additional money or power. You can still vote for the candidate you prefer, regardless of party (or lack of party) in the general election.
By registering for the majority party, voting for the candidate closest to your position in the primary, and voting for the other party in the general election (especially if the candidate you voted for lost), you're forcing the primaries, which are currently controlled by partisan extremists, to shift more towards your view and moderate their extremism and partisan loyalty.
This only applies to the states with closed primaries. In semi-closed states, you should just be unaffiliated.