Maybe not in BG2 where the battles are rather lop-sided, but in similar games like IWD, which is more combat-oriented, rest assured that about 90% or more of my battles results in a loss of more than 75% of HP.
In BG2... I have "suffered" similar cases with a solo Kensai( 2HP left, woot), a solo Paladin( 1HP left, hahahaha, *whew*), even with a solo Sorcerer( 10HP left). So you are wrong if you think I have not experienced such situations. Ideally in a perfect world, it will not happen, but we do not live in a perfect world. More HP is always welcome, so long as the source is legitimate.
Maybe for those who play on Core Difficulty and on a Default Installation find no need for a "mere" +12HP, but for nuts who play on HoF Mode, Insane Difficulty or with Mods, +12HP is a valuable asset. It can literally mean the difference between life or death.
If you have 60HP left( reasonable), and the enemy deals 60 damage( usually more
), you die. With a HP boost, you live. It is that simple.