The suggestions always work in 4 "stages" - "no issues", minor issue, average and major, based on the thresholds given. I'll start with Affliction because it seems like the most popular and played spec (and also the first I made).

Agony uptime (without WiA):
	100% - 85% - no issues
	85% - 80% - minor
	80% - 70% - average
	<70% - major
	suggestion: Your Agony uptime can be improved. Try to pay more attention to your Agony on the boss, perhaps use some debuff tracker.

Agony uptime (with WiA):
	100% - 95% - no issues
	95% - 90% - minor
	90% - 80% - average
	<80% - major
	suggestion: Your Agony uptime can be improved. Try to pay more attention to your Agony on the boss, especially since you're using Writhe in Agony talent.

Corruption uptime (without T20_2pc):
	100% - 85% - no issues
	85% - 80% - minor
	80% - 70% - average
	<70% - major
	suggestion: Your Corruption uptime can be improved. Try to pay more attention to your Corruption on the boss, perhaps use some debuff tracker.

Corruption uptime (with T20_2pc):
	100% - 95% - no issues
	95% - 90% - minor
	90% - 80% - average
	<80% - major
	suggestion: Your Corruption uptime can be improved. Try to pay more attention to your Corruption on the boss, which is especially important with the T20 2-piece set bonus

Siphon Life uptime (if talented):
	100% - 85% - no issues
	85% - 80% - minor
	80% - 70% - average
	<70% - major
	suggestion: Your Siphon Life uptime can be improved. Try to pay more attention to your Siphon Life on the boss, perhaps use some debuff tracker.

Mobs sniped - counts the amount of adds we sniped with UA/DS (at least one of them) for bonus shards. Also shows the actual number of shards sniped (NOT counting wasted ones) and the theoretical possible number of shards (assuming UA+DS on every one of them which is pretty much impossible on fights like DH, DI, Harjatan)
	100% - 90% - no issues
	90% - 75% - minor
	75% - 50% - average
	<50% - major
	suggestion: You sniped X % of mobs in this fight (X / Y) for total of X Soul Shards. You could get up to Y Shards from them. Try to get at least one shard per add (cast Drain Soul on them before they die) as it is a great source of extra Soul Shards. Note that the number of adds might be a bit higher than usual, as there sometimes are adds that aren't meant to be killed or are not killed in the fight (such as Tormented Soul at the Demonic Inquisition fight).

UA buff tracker - shows the amount of UA ticks that are unbuffed by Reap Souls and/or Haunt/MG
	0% - 15% - no issues
	15% - 20% - minor
	20% - 25% - average
	>25% - major
	suggestion: Your Unstable Afflictions could be buffed more. Unstable Affliction is your main source of damage so keeping it buffed as much as possible with Reap Souls, Drain Soul (if using the Malefic Grasp talent) or Haunt (if using the talent) is very important.

Soul Shards wasted - I personally think that no shards should ever be wasted under any circumstances but Zero is a big fan of metrics that are dependent on something, like a fight length, or percentages, not fixed amounts. So to comply, I'm tracking shards wasted per minute (as it also makes some sense that 3 shards wasted in a 3 minute fight is much bigger deal than 3 shards wasted in a 10 minute fight). I've got these initial suggestions from a guildmate and I didn't have any better so I went with it.
	0 - 0.5 - no issues
	0.5 - 1.666 - minor (5 shards per 3 minute)
	1.666 - 3.333 - average (10 shards per 3 minute)
	>3.333 - major
	suggestion: You are wasting Soul Shards. Try to use them and not let them cap and go to waste unless you're preparing for bursting adds etc.

Empowered Life Tap uptime (if talented) - this module currently has a bug (also present in Destruction as these are identical) where it shows 0% uptime and 0 bonus damage if you actually kept a 100% uptime (pre-combat Life Tap and never let it fall off), this is currently because of technical issues and could be perhaps fixed in the future (till then I've included a small note explaining this behavior)
	100% - 90% - no issues
	90% - 85% - minor
	85% - 80% - average
	<80% - major
	suggestion: Your uptime on the Empowered Life Tap buff could be improved. You should cast Life Tap more often.

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On top of these custom suggestions, there is a Cast Efficiency tab, where we specify certain spells and it automatically calculates the maximum possible casts (there's still some work going on in there with respect to haste buffs and trinkets and all those shenanigans) and actual number of casts and shows a suggestion if it falls under a certain percentage. That percentage is 80% unless specified otherwise by us. We can also choose to turn off these suggestions or not show the orange "Can be improved" text. Zero insisted we put all the spells in there, even the not useful ones (I don't think it's necessary how many times I've cast Unending Breath but be my guest), but the ones that matters are configured this way:

Haunt: 95%
Phantom Singularity: 95%
Agony, Corruption, Siphon Life, UA, Drain Souls, Life Tap, Seed of Corruption - don't show suggestions or can be improved (so basically just counts the amount of casts)
Soul Harvest: 80% (I think it mostly has to be planned, not blown on cooldown)
Doomguard/Infernal if untalented: 95%
Grimoire of Service: 80%

all other spells are without suggestions or improvement
NOTE: Reap Souls is intentionally left out, as I've been told it makes the impression that it should be cast on cooldown (which a text like "11/59 casts" could imply) which is not the case