I believe (don't quote me here) that 3/8, and certainly 6/8 have a different 'feel' to 3/4. 6/8 is more like two groups of three, e.g. 'ONE-and-a-TWO-and-a ...' (think 'Angel of Music' from Phantom of the Opera), whereas a waltz is more 'ONE-and-TWO-and-THREE-and ...' and in 3/8 you're looking at a slightly different 'ONE, two, three ...'.
Generally I don't question it. I just note the tempo, watch the conductor and get on with it and it usually comes out right in the end.