boiling removes all the dirt and grime n grease from the strings, and stretches/shrinks them with the heat, making the strings fresh n zingy again. i usually follow up with a quick bake in the oven for 10 mins at 200 degrees to dry them off n finish the effect
obviously wont last as long as new strings, but you can do it several times before it loses its effect, saves alot of money
boiling will not soften the strings at all, if your not getttin on with steel get nickle
although warning, do not boil nickle strings in the same pan as you cook food in, itl leave a nasty residue and your food will taste funny!