Too good an article to miss: http://www.theviolinchannel.com/vc-masterclass-vc-young-artist-augustin-hadelich-training-left-hand-vibrate-like-singer/
I believe it is extremely important for you to will your hand to do exactly what you want it to do in a phrase – and in such a way that it will sound more like a singer.
A good example is in the Bruch Violin Concerto opening where the 2nd finger falls on a lot of weak notes, but often I hear people vibrate the 2nd finger the most – where the vibrato should, in my opinion, be growing towards the suspensions.
~ Augustin Hadelich
His playing in the video illustrates his point excellently: