A buddy and I are playing through, myself as a wind druid and him as a summoning necro, and we're debating which to use and at what times.

I was thinking decrep on bosses and amp dmg the rest of the time.
He thinks they will already be slowed enough by his golem and merc decrepify won't be a big benefit.
I say the big benefit will be lowering the enemies damage output and physical resist.
To which he counters, amp dmg lowers resist even more.
etc.
etc.

Anybody with more experience willing to chime in on this debate? I'm not a necro guru.

Thank you!

As long as survivalbility isn't a problem use amp. If you ever feel like you're risking your life(assuming this is hardcore) start using decrepify. Basically Amp = more speed and Decrep = more safety.

A good summation

Thanks Flame-Masta!