I think you would end up with false relevance values.
Suppose, against the same index, you run 2 searches. The range of relevance scores from the first search range from .0001 through 1.5000, and you scale that so that it's between 0 and 1. For the second search, suppose the relevance score range is between 0.0500 and 3.5000, and you scale that from 0 through 1. Now you have two result sets – and you might think that the highest scored result from each of the searches, now having a relevance score of 1, have the same value – but they don't. You have artificially scaled your two individual result set relevance ranges into the same 0..1 range. You've lost the original relative scorings that would let you actually compare the top result of each of the searches, because the scaling you apply to get rankings between 0 and 1 isn't constant across all searches.
Bob Sandiford | Principal Engineer | SirsiDynix