During the seventh and the eight century CE, certain linguistic changes took place in Scandinavia requiring some transitions to occur in the writing domain, as well as in the phonetic one. Similar linguistic processes in England had caused the enlargement of the rune row. But in Scandinavia there was a strong tendency to simplify it. The most complex symbols of Elder Futhark were removed and the runes with two upright staves were reduced to only one (for example, the rune Hagalaz). Through the history of linguistic forms, alphabetic rows have always tended to shrink, because they are by definition very abstract symbols of spoken languages, but a smaller unit than a sound doesn't exist in any idiom, which is why there isn't an alphabet in the world today that consists of less then 24 letters. This is why the transit to shortened rune-row, from a linguistic point of view, is so strange - there suddenly weren't enough written symbols to be added to each sound.
The Younger Futhark, which include both Danish and (probably later and even simpler) Norwegian-Swedish rune rows, that differ only slightly, was in use all over the Scandinavia during the Viking-age, which started off with the attack upon the monastery of Lindisfame, in northeastern England, 793 CE, and diminished around 1350's. This era produced many Viking-settlements in Ireland, parts of England, Normandy, Iceland and Greenland. They even found the state of Russia, the name of which literally means 'the cities' in Old Norse. All these areas spoke that language, split in two groups - West Norse(dialects - Old Icelandic and Old Norwegian), and East Norse (dialects - Old Danish and Old Swedish), but these were all very similar, and therefore, they all used similar writing rows - Younger Futhark .
By the 13th century, languages of Scandinavia dispersed and than again recombined into new Danish tongue ('donsk tunga'), but soon had become permanently incomprehensible to each other.
Most people, when using the term Old Norse refer specifically to Old Icelandic, even up to the language of 16th century because it produced and preserved the most interesting manuscripts. Because of its political and strategic position, Iceland made the least changes in its language until today of all the Scandinavian countries, and its tongue is the most similar one to the now extinguished Old Norse.
Therefore, the language once used for writing in Younger Futhark is well known to the mankind from a great number of rune-inscriptions all over the northern hemisphere, and the customs and environment of those who were using it is known from preserved literature. This is very useful in making the runic spells because the magical values can be increased by using their original language.
A modern rune-master will normally choose the 24-rune row for divination, because it is the original, the most ancient, and for these reasons, the most mystical one. But some consider the Younger Futhark more adequate for magic, because it is even more symbolic than the previous one, and its shortage as an alphabet (derived from a longer one, which was more useful for writing) implies the greater divine meaning. Still, if you rather use the Elder Futhark, at least take a look at the meanings of these symbols trying to connect even more with the reflections of the ancient pirates of North. When they were deciding to sail towards the other end of the Atlantic Sea, they obeyed the counsel of the 16 rune-row.
As letters, most of these runes were accompanied by several sounds. For example, the word Viking-'wikingr'was written (u-i-k-i-k-r). Or, the word (d-r-i-k-r) can mean either 'young man' (draengr) or 'drinks' (drikkr). You can notice in these examples that two of same letters in a row weren't repeated in scripture, and that the rune Kaun replaces four pronunciation sounds - k, g, nk and ng. Like sounds, the meanings from some of the disappeared runes were added to the remained ones, some were modified, and some erased. Three runic poems exist to describe the Younger Futhark -a rune poem in Old Norse from Norway, the one in Old Icelandic from Iceland, and a very simple one - 'Abecedarium Nordmandicum' in German (9th century, the oldest record). These poems are a type of memotechnique for easier remembrance of runes and their meanings.
The Vikings soon started to amplify the alphabet with 'stung' runes - letters with dots that slightly changed their phonetic value (iss with a point was pronounced 'e', kaun with a point 'g'...). These symbols didn't have any value in divinations, but in Sweden they extended to 25-rune row, arranged in the order of the Roman alphabet.
In the 13th century, runes, mainly the 'pointed' version, were being written on parchment, became rounded, and their usage continued up until the late 18th century in Sweden in some manuscripts and correspondence, and also on wooden church inscriptions (because their shape made them easier to carve, once more).
The most simplified form of all the rune-rows in history were the 12th century staveless 'Halsinge Runes' which had lost almost every upright line. They were meant to be shorthand writings for everyday-life usage. These also derived from the Younger Futhark.