Burning Hands is the fun spell you cast when the target is 100% immobile and harmless. For example, to finish off a Troll that has fallen after being beaten to the ground.
Or it's one of the spells you use regularly, if you have chosen say a F/MU who specializes in close combat and touch spells. Perhaps such a character *likes* to mix it up and get in enemy's faces while laying down Ghoul Touches and Vampiric Touches....
There are as many ways to play any of these games as there are players and the only "right" way to play is the way that entertains the player the most.
I'm all for explaining the easy way to play to people, i.e. ranged attacks, having the mage hide at the edge of battle and so on - these suggestions for newcomers make sense, without a doubt. But it should be kept in mind that this is *not* the only way to play, nor is it the only way to play a Mage or any other spellcaster.
My Blade, for example, rarely if ever has any Mag Misl spells memorized - just personal preference.
It also depends on the game, of course. Xan's ability to cast Sleep multiple times per day, taking out numerous *multiple* enemies at once, is, IMHO, vastly superior to Dynahier's ability to cast multiple Magic Missiles - which target only a single enemy. Sleep will remain useful throughout most of BG1 [it will work against Black Talon Elites, for instance], while Magic Missile is really only important and "better" with regards to taking out mages... Which is a big reason why I rarely take Dynaheir in my party....
Yes, Magic Missile is fast, does decent damage and can disrupt spell casting. Burning Hands is equally fast, does decent [and less variable] Elemental damage and can also disrupt spell casting. At say PC 3d lvl, a Magic Missile spell does a range of 1d4 + x2 damage, or 4 to 10 points, or an average of 7 points per casting.
A 3d lvl Burning Hands does 1d3 +6 or 7 to 9 points of damage, with an average of 8, or, if saved against, 3.5 - 4.5 damage, with an average of 4. Not a significant difference really, IMHO, since the variable number in BH is small [the single 1d3] while the variable number in MM is large [*all* 1d4 rolls].
At 10th lvl of ability [equally max for both spells], the MM does does 5x 1d4+1, or 10-25 points of damage, with an average of 17.5. BH does 1d3+20, or 21-23, with an average of 22, or 11 if saved against.. Considering that at 10th lvl, one assumes you have ways of lowering enemy saving throws on a fairly routine basis, the difference in expected damage is again not that significant.
The point being that there are many ways to look at spells and decide which is the one *you* enjoy most, or value most, or prefer. Some of this comes down to game mechanics, i.e. MM is "better" because it is ranged, say, but the fact that it *is* ranged might not appeal to a player or their character, if they want to fight toe to toe employing touch based spells. After all, there is more to the game than just what X person or group says about what action or choice has the most "utility"... :) Just one man's opinion, of course... :)