While it may not seem like a big deal to the average person with only a half class of one bottle left and a want for a glass of wine. Pouring the remainder of that bottle in with a little of the new bottle though can actually be seen as an insult to winemakers and even devout wine drinkers. This is not to say that it is a bad habit, just be aware that not everyone will want to drink mixed wine and that the mixing may not always turn out good. A wine is already a delicate balance of so many compounds that mixing it with another wine is really a roll of the dice. If two flavors or compounds clash with each other or if the two wines have high levels of one flavor, the result will take on a very unpleasant unbalance. There is a place for wine cocktails, a good mix can be perfect for parties, but make sure to let guests know that it is not all of the same wine. It would be a disappointment to a guest to ask what the wine was and have to look through three bottle wine carriers.