Everyone knows they need to rest meat after cooking so that the juices don't run-out when they cut it. So why do so many people tear their steak apart with serrated knives that leave the juices all over the plate instead of in their mouths?
The cutting action of serrated knives rips and shreds meat to create the cut. This produces a traumatised region of tissue with a very large surface area that allows a high rate of fluid loss out of the cut surface and onto your plate.
Steak knives with a straight edge create a far cleaner cut that has much lower surface porosity, resulting in fluid loss that is extremely limited compared to cuts created with serrated edges. They can also slice meat into much thinner portions, giving you that melt-in-the-mouth experience.
So why are serrated edges on steak knives in the first place? A combination of convenience and 1970's BBQ techniques.
If you were around in the 1970's then you'll no doubt recall that most people enjoyed their steak somewhere between "well done" and "car tire." Steak of this consistency necessitated the use of serious quantities of tomato sauce and cutlery that could see double duty pruning tree branches. Fortunately, society today is more conscious about combining quality ingredients with the correct cooking techniques; unfortunately we're still playing catch-up when it comes to cutlery.
A plate is about the worst cutting surface anyone could dream up - it's hard and will turn the edges on sharp knives rather quickly. Serrated edges also suffer from turned edges, but only on the 'hills' of the edge; the 'valleys' of the serrated edge never touch the plate and these are the parts of the edge that perform the bulk of the cutting work.
If you use steak knives with a straight edge you are going to find yourself sharpening them on occasion. This isn't as onerous as some might think: it only takes a few passes on a honing rod after each use to keep an edge well maintained. This means that the practical difference between serrated knives and straight edge steak knives is a little know-how and a few seconds of maintenance after each use.
Serrated steak knives are similar to stainless steel in that they trade quality and performance for convenience. This has caused many people to forget how great carbon steel knives are, much the same as cheap serrated steak knives have lead us to forget that there is a better way to eat steak. It seems such a shame that people spend so much time and effort cooking wonderful cuts of meat only to rob themselves of the full-flavor by using sub-par cutlery.