Not all wines, of course, have residual sugar, though all have some acidity. Sugar-acid balance is thus limited to wines which have an interplay between these two elements. There is no accurate formula for calculating the perfect acid-sugar balance in a wine, despite the fact that there are some people who advance that very notion. By extension, a wine which is out of balance has either too much acid or too much sugar. A wine with too much sugar will taste cloying, sugary and flabby, and will not refresh the palate.
Some wines have too much sugar and acid.
They are often the result of a winemaker trying to balance a high acid with additions of sugar. These wines don't work, because the other elements if the wine, especially 'extract', don't match the sugar and acid. Experienced tasters often describe such wines as having a 'sweet-tart' character. Another important balance is that between alcohol on the one hand, and acidity and astringency on the other. This is obviously most relevant to red wines.