The idea behind the party platform has definitely seen some recession over time. The previous thoughts are accurate on this. Yet, I do believe that there is some level of mutual dependence that candidates and political parties share. There have been occasions where the party platform is secondary to political expediency. Senator Lieberman and Senator Specter are two recent examples where the political party's concerns were secondary to the need to remain politically viable. Their switches to different parties did not reflect much in the political platform. Yet, candidates who reflect and use the name of a party are required to make some concessions in embracing the party platform elements. The party no longer exerts the kind of influence that it once did in American politics, as there is more freedom for candidates to "buffet style" the platform and embrace some elements and not others. Yet, the overall and general timbre of the platform has to have some resonance with the candidate. The presence and appearance at the conventions are symbolic, but highly meaningful. For example, there was a large outcry when the aforementioned Lieberman gave a stinging speech against the Democrats at the Republican National Convention. The calls for rebuke and some type of silence were prevalent when the Democrats won. At this instant, party platforms and political revenge had merged. The platform itself is not as important, but it still holds some level of viability in terms of party members who do embrace much of it.
Great posts above. Also, in formulating a party platform, there is a process that starts at the precinct and county level, then works up to the state and national conventions. Delegates present at each of these levels can vote yes or no to each proposed "plank" or policy statement. So you end up with 50 platforms from the states, and these are consolidated and weeded through at the national convention during the week until a national platform is adopted.
I have been in on the first two levels of that process, and it is both interesting and encouraging to see a democratic idea form at the grass roots level. At the national level during an election campaign, and in the modern day of internet/tweeting/YouTube and television, parties don't need to be as clear in their ideas as they used to be. So platforms aren't talked about that much.
One of the things that party platforms are used for is to persuade voters to vote for a certain candidate based on an understanding that the candidate will stand for those things once elected. The current set up of parties and elections does not particularly allow for independent candidates to run for office so a candidate must align themselves to a particular party and their platform in order to have an opportunity to be elected.
It also gives people who are not able to take the time to fully investigate a candidate the opportunity to choose a candidate based on their party's platform assuming that they again will know what that candidate might work for if elected.
Party platforms are something that no longer mean what they used to. The party platform is a statement of what the political party believes. This is supposed to serve to guide people in the party.
However, this is now only really a symbolic thing. No person who is running as a candidate for some party's nomination is required to agree with everything (or anything) that is in the party platform. Candidates run more or less on whatever they want to emphasize - not what the party says is important. This is why one government textbook's site can say
Party platforms are drawn by the delegates at both national conventions to set out the party’s goals and policy positions in a largely symbolic way.
So it is really just something that the party cranks out because it is traditional. Because of this, you really don't hear much discussion of what's on the platform the way you used to.