Most fonts will require kerning, except for monospaced fonts or icon/dingbat fonts.
Kerning and letter spacing are not the same thing. “Kerning” refers to pair-specific adjustments to the space between two characters. Most often, a kerning pair is added to a font to reduce the amount of space between two characters (“negative kerning”). A common example for the application of a kerning pair would be for the space between ‘A’ and ‘V.’ Typically, both ‘A’ and ‘V’ would be spaced so the terminals of their diagonal strokes nearly touch the vertical stroke in the adjacent letter, like an ‘H.’ When a ‘A’ and ‘V’ are set next to each other, however, the spacing looks too open. There can also be instances of “positive kerning,” where additional space is added between two characters.
When you apply kerning to your font, do it systematically. If the uppercase ‘A’ is one of the letters used in a kerning pair, for instance, the same kern may also need to be applied to all instances of the ‘A’ with diacritics, as well as to any formally-related characters present in your font. Also, don’t forget to look at punctuation. In most cases, fonts will need kerning pairs for many uppercase letters + punctuation marks, lowercase letters + punctuation, numerals + punctuation, and even between pairs of punctuation marks themselves (e.g., the comma followed by quotation marks).