Fading and resurrection

I've heard, that elves go through several life stages over their multi thousand year life span. At the end of that, they start to fade away. Or atleast their body.

On the other hand, i have heard, that a dead elf can come back from the halls of Mandos by getting a new body.

What is the point in fading, if they simply respawn after that anyway? And do the new bodies fade aswell eventually?

Also, elves, or atleast their souls, are bound to the lifespan of arda. They will eventually all die anyway with the planet. So why the whole fading thing? Why don't they simply live on till the end?