@mangle vs shred
there really isn't a reason to use Mangle - the 5 less energy cost is unnoticeable, but the lower damage for not having a bonus for bleeds is more noticeable. Regardless of what percentage of your damage it would be, by NOT using mangle, you're essentially losing damage by choice -- or otherwise just not maximizing your DPS, which happens to be what most DPS are compared against (how much damage you can do, how good are you at avoiding stuff, or quick you are to BRez, off-heal, interrupt, or do anything else that isn't involved with dps).
I used to use this mostly cuz I didn't want to bother with DoC (not that I couldn't, I just didn't like it). But I changed my mind for Tier 15 and have seen a fairly modest gain.
I'd go so far to say Incarnation really has no place in heroic raiding (where low DPS will be penalized most). The only exception I can think of is Heroic Elegon early in progression, where a skilled group of DPS could push him into the first spark phase before 2 big adds came out better/easier with Incarnation (but then as soon as you got geared, you could end up doing more damage with SotF/DoC).
@renataki's trinket//trinkets in general
With renataki's you do know you have about 18 seconds to get things lined up for the 10th stack of it, right? That's almost twice as long as Pred Swiftness, plenty of time to get 5 combo points at minimum and pool some after it, and a pretty good chance to see TF come back up. I've even taken to holding NS+HT for when Renataki's procs.
For most other trinkets, I'd highly suggest to make weakaura's, or other noticeable cooldown/proc/buff tracking mods. For Renataki's particularly, since it's proc stacks, have 1 weakaura show for 1-4 stacks, duplicate, 1 weakaura for 5-9 stacks, duplicate, 1 weakaura for 10 stacks. Or if you knew a trinket had an ICD, you could make a weakaura for it to know when it could proc again. Really, WeakAura's is a hugely useful addon.