(only partially related to the 'can't improve on a limited source' idea)
For me, with music, striving for another few %.... "Good enough" is a price point.
Yes, I want the best bang/value/sound for the money.
Yes, it takes exponentially more money to get another couple % "improved" sound.
Yes, passing my budget limits makes me reflect, is what I have "good enough"? (And, did I spend wisely, in the right places? Unfortunately, you have to ride the merry-go-round for a while in order to gain the wisdom to even guess at an answer. Or follow the advice of others who've been riding longer than you.

)
For these reasons, I read and read about dsd/pcm for example, and wonder how close to that bleeding edge do I want to get. (side note... I just broke down and got on spotify...and I tell you, the convenience of having so much so accessible even at lower quality... it's reduced my drive to build my lossless music collection)
5% from the goal line can look like eternity.