Killing the bosses make only sense if you really need their stuff.
Why should one make the Meadows harder before he has a upgraded Crude bow, flint knife and full Troll Armor. (and as sideffect 12+ Surtling Cores)

Sure thats not necessary to kill elder, but you have less annoying mobs in the meadows

So its a good preparation to start mining, and thats the point you need to kill Eiktyr