I have thought a bit longer about this and I think I have come to the essence... the essence of the advantage absolute grading has over relative grading (in which every grade has to be awarded, to cover the total spectrum).
In short: an absolute grade really says something about the individual like factor of a song, on its own. It defines judgement. It summarizes a total of negative and positive aspects.
I'll show it with some examples:
If two people vote "the relative way" and both give a 1 for the same song. What do we know? Do we know that this song sits at the very bottom of all Maiden songs, for these persons? Or do we know if the song sits in a group of 10 or 20 or 30 Maiden "least" good songs? If someone terribly hates Maiden, more than half of the songs could have a 1. One person could see the song with a 1 as one of his least favourite songs, but still doesn't avoid like the plague, like the other person is doing, cursing it (with his eye) and hating it terribly much. So what do we know? We don't know. In theory, we know nothing. Apart from a ranking of a song in the total. But we do not really know the context. We do not know why a song is at a certain position. It's the total of unknown subjective randomness. We do not know what someone thinks about a song. There's is no individual aspect to be deduced.
If one person votes "the relative way", e.g. gives a song a 2 because the song is in the top half of his lowest 20 percent (or whatever subjective own other method is used) of all Maiden songs, but still this person tolerates it, and stamps it as "unsufficient", or "weak"..
And another person does it "the absolute way", e.g. has the same feelings about the song, but gives it a 4 or 5...
Then what do we know? With the first person we cannot see from the grade how he likes the song. At most, we could try to see a position in someone's ranking, although we do not really know it, because we do not know how the distribution of grades is done (e.g. the following is possible if we pretend Maiden has 150 songs and an even distribution of grades is desired: 15x10, 15x9, 15x8, 15x7, 15x6, 15x5, 15x4, 15x3, 15x2, 15x1, but there are dozens of other possibilities).
We can see it from the 2nd person (if some known system is used). But what is such a mix worth? Not much either.
So in the end, it's the best when everybody uses absolute -generally known- definitions for grades. This way, we both can value the individual appreciation, and the total.