Districting is a Constitutional requirement that must be done every ten years following the census.
The requirement has become a political tool. It is believed that If one can corral many of one's own party into one district, reaching them will be easier. This assumption guides most if not all of the planning of those who refer to themselves as "Politicals."
"Politicals" generally are campaign managers, lobbyists, and candidate promoters. Through a variety of marketing techniques, they promote a given candidate either for pay and/or for conviction. That means they spend money. And that means their central concern is how to get the biggest bang for the buck in order to get their candidate's name recognized and ultimately elected.
For this reason, some statistics are considered important: (1) It is widely accepted that 20% to 25% of the electorate vote the straight ticket;
(2) if many of the same political party are corralled into one district, that district is thought to be assured of 20% - 25% of the vote for the party. The advertising dollar thereby does double duty as it focuses on the other 75%. Districting in one party's favor is thought to make more effective use of campaign money.
Whether districting does or does not help a given political party, ask yourself who does most to get out the vote? Individuals who want their candidate to win and are willing to talk to others to elect him or her.
Who is the electorate today? It is not only Democrats and Republicans. It comprises a significantly large number of Independents or DTS and other parties. And it comprises many that are registered as one of the foregoing but who in fact stand for individual rights, limited government, free-markets and fiscal responsibility. In other words the principles that guide most Tea Party supporters---whether they call themselves Radicals for Laissez faire Capitalism, or Classical Liberals, or Conservative, or Democrats.
Surely, if most of one's party is in the same area, then one can reach them more easily. But reach them how? Ultimately the electorate is reached by the individual precinct captains, individual ward chairmen who organize and motivate the individual neighborhood walkers to go door to door and explain what a given candidate stands for and why voting the straight ticket is detrimental to one's self-interest.
How does one persuade an individual to refrain from voting the straight ticket, and instead to vote for individual candidates? Would you buy a quart of strawberries if you saw that some of them were rotten? It's the same idea with voting the straight ticket. If you vote a straight ticket, the danger is you'll be voting for a number of rotten candidates. Better to vet men individually. The collective approach is never a good idea in anything.
For those who would like to learn more about districting, I recommend the following web site where you can download a number of documents dealing with aspects of it. http://www.janicearnoldjones.com/Redistricting/tabid/180/Default.aspx