One tactic used by both sides is some sort of breathless announcement that some Federal Election Commission Filing Deadline is coming, and if you don't donate RIGHT NOW then all is lost, FOREVER LOST!
I long ago brushed this off as some sort of blatant political promotion to try and GET MOAR MONEY! from the loyal masses, but it crops up with such regularity that I decided to do a little research.
So … the FEC has various reporting dates over the course of the year (http://www.fec.gov/info/report_dates.shtml) by which campaigns, parties, PACs, etc. have to report money given, spent, etc. This is moderately useful both for transparency and to ensure that if donations are being done improperly that it will generate a nasty memo from the FEC in a year or two.
More importantly, the FEC reports this information to the public (transparency, remember?), which is then highly useful to the political parties themselves and the supporters of various candidates, as a means of seeing what sort of financial support the opposition is getting. The idea is, if Richie Republican is squaring off against Donna Democrat, each side is very interested as to how much money is being plowed into the other side's campaign, to determine where to spend its own money, which campaigns to give up on, which ones to double down on, etc.
Generally speaking, if Donna Democrat's campaign has a lot of money plowed into it (indicative of broad, or a least deep-pocketed support, and thus an ability to massively spend on a wave of commercials), it might tempt the GOP to give up on Richie Republican, which not only counts as a "win" for the Dems, but frees up other money and staff to be exerted in other races.
Alternately, if Donna Democrat has been campaigning like mad, but the money just isn't coming in, or donations are down, it might convince the GOP to crank up the spending screws there on Richie Repulican's behalf against a failing opponent (or, alternately, to interpret that race as already won and pushing that money to tighter races). It might also convince the Dems that they should stop throwing good money after bad and write off Donna as a lost cause.
So, yes, a lot of the DREADED DEADLINE DOOM is just trying to pressure you into sending in money (always need more money, y'know) — but there is a certain strategic advantage for both parties to finish a reporting period with big numbers showing up, and to be able to gauge how deep the financial support for candidates is (and, thus, might be the next time they ask for moolah)..
