Q: What are masterwork rolls?
A: Most legendary weapons are capable of being Masterworked. The masterwork system is a way for you to upgrade your favorite weapons to their maximum potential.
Q: What does it take to upgrade a weapon to a masterwork?
A: Upgrading your weapons, in broad terms, takes a small amount of glimmer, legendary shards, and, most importantly, Enhancement Cores.
Depending on what Tier your weapon is at, the requirements to raise it to the next tier increase the closer the weapon is to being fully masterworked (Tier 10).
Q: What benefits do I get for masterworking a weapon?
A: Each tier that you increase your weapon will grant a small buff to a single stat, chosen randomly when the item drops.
Beyond that, at Tier 5 you gain access to a kill tracker. At Tier 10, your multi-kills will generate orbs of light.
Q: So what are these "masterwork roll" stats?
A: These are the possible stats that upgrading your weapon will grant a bonus to. Depending on what tier you are at, you can grant anywhere from 1-10 additional points in any of the stats listed to your weapon.
Q: Any catch with this?
A: The Bungie API currently says that all weapons can potentially roll with all stats as their masterwork stat. This obviously isn't accurate, as Blast Radius isn't applicable to, say, Auto Rifles.
The list you see on this page is trimmed to only show stats that actually appear on the weapon. However, it is possible that Bungie has additional logic behind the scenes that further filters these
possibilities to, for example, prevent certain items from being able to have an Impact masterwork. Until Bungie modifies the API files to 100% accurately display which masterwork stats are possible on
each item, take what you see here with a pinch of salt.
Let's say you are a T8 Intellect Warlock running Well of Radiance in Trials. Your super comes back in 363 seconds (6:03) from the passive regen. One kill with a Thresh weapon will reduce that time 3.6 seconds (more like 5 if it's one of the listed special weapons). If you get 5 kills, you'll get your super back 18 seconds faster than kills with an otherwise identical weapon. Seems good, right? Lots of rounds don't last that long.
Problems:
1. Dealing and taking damage and getting kills also grants you super energy. These are also going to mitigate your super cooldown, and will be a much bigger portion of that than Thresh, so you're better off using perks that will actually help you win fights and reap the super energy rewards from doing that.
2. Upgrading to T10 Intellect is a 15 second faster regen. You'd sacrifice some other stats doing that, but if it means you can run a Real Perk(tm) on your gun, it seems pretty worth it. If you're using a slower super or if your INT is a little lower, the difference becomes even more dramatic.
And in the PVE case, with how fast you can get your super back in that context, you won't even notice it's on the gun.