The tail piece are an essential element to any violin, without it there is nothing to hold the other end of the strings tight with. Traditionally the tail piece is made of ebony or another timber like rosewood. Traditionally strings were all low tension gut, so tuning up at the scroll end with pegs was no big deal.
However today we have much high tension strings and so it means there is more need for micro adjustments, so it’s a bit trickier up top. This is especially true with the E string which has the highest tension of all the strings.
So along came the fine adjusters to be added to the tail piece, which you often see on all strings, just the E or the A & E string. Why is in not on all strings rountinely? The problem is fine adjusters add weight to the tail piece and this is thought/shown to alter the tonal qualities of a violin. While the strings vibration is mostly on the other side of the bridge, there is a contribution from the tail piece side and extra weight meaning extra dampening of the vibration.
A committed player thus might just have a E string fine adjuster then and happily adjust all the others at the peg box end. The A string is a little tricky to adjust with the left hand for many, as keeping the peg pushed into the peg box and turning it ads an extra level of finese required. On many instruments out of the factory you will see all four with fine adjusters ….the manufacturers thinking is probably “let the player decide how many to keep on their violin”. Fine adjusters then also become something of a ‘signal’ to other players as to how advanced you are in your playing. Having just one is more traditional, thus looks way cooler, as you demonstrate your knowledge of knowing about tail pieces weights and its effect on your sound (imaginary or otherwise) to seperate yourself from the pack.
Enter the inbuilt self adjusters, these tailpieces come in at the weight of a wooden tailpiece – without the weight of the fine adjusters, the fine adjusters are also more discrete so you can’t see them from a distance. Purists don’t tend to favour them out of tradition, but also about concerns about the resonance characteristics in wood tail pieces being superior to any modern material.
For students the convenience of inbuilt fine adjuster tail pieces I think out weigh the aesthetics, also people playing outside of classical traditions tend to favour them as they are much easier to do a quick tune on in a band situation. They are a fairly quick thing to swap over and not to expensive either at ~$20 for an entry level one.
Getting fancy there are tailpieces with variable string lengths to the bridge to help with the tone production of each string. Lower notes have a longer wavelength and this give the tail piece side more room for them to swing. I’m not convinced but hey on an instrument as standardised as a violin and being one of 20 violinists in an orchestra, having some self expression and individuality on your instrument ain’t a bad thing and gives you something to talk about at the after party 😉