My lock is level 68 and I was looking at the Oblivion Raiment item set and noticed the Improved Seed of Corruption 4 set bonus.

Your Seed of Corruption deals 180 additional damage when it detonates.

So then I started looking into it more because this item set has the only direct modifier for SoC in TBC which is the primary AoE spell for warlocks, I wanted to know if there's a meta for keeping that item set in bags for big trash clears and aoe fights.

There really isn't a lot of discussion around it but there's a few places where it was brought up.

The oblivion set remains the BIS “seed” set and trash set until haste come into play iirc. And even then I think it was still worth wearing and forgoing haste in the set slots.

Source: reddit.com/r/classicwowtbc

the 4 piece bonus is crazy good for every situation where your main dmg spell is seed and you are not aoe capped: trash, dungeons, but also raidbosses like Moroes and Illhoof. Every single target that explodes gets the +180 (base) bonus dmg. Therefore it feels like wearing an extra 800 spelldmg when seeding!
Lassive

Yes! Glad I stumbled on this, was trying to confirm this fact. I vendored my whole 5/5 oblivion set bc i've gathered better gear from heroics and raids. Then this thought occured to me, "holy @#$% +180 dmg on aoe spell is nuts if it's flat dmg, not +sp!" I just restored the whole set last night, haha. I think this actually has amazing utility if you're willing to carry around the set and if you get the ItemRack addon to make swapping it in and out ez pz.
Bernoulli

Source: Wowhead

More importantly Zephan talks about it in his Warlock AoE DPS guide on Wowhead. While the guide hasn't actually been updated since the original TBC Classic in 2021 other than a minor edit, Zephan's been one of the leading Warlock theorycrafters and had this to say.

The four-piece set bonus of Oblivion Raiment adds 180 flat damage to your Seed of Corruption explosion. What does this mean really? If you know the explosion has a spell coefficient of 21% then you would need 841 Spell Damage to reach the same amount of damage bonus. (841 * 21.4% = 180). This makes Oblivion Raiment the best gear to have if you are dealing AoE DPS under the AoE Cap. The Set bonus does not forgo the AoE Cap as has been tested here. It does scale with crit just as spell power otherwise would.
Zephan

Assuming the AoE stat priorities mentioned by Zephran are correct it seems as though combined with a specific AoE talent build it should last the entirety of TBC except for maybe Sunwell when there's more haste gear but stacking crit on top of Imp SoC might still perform better.

• Spell Hit Rating (Until Capped)
• Spell Haste Rating
• Spell Crit Rating
• Intellect
• Spell Damage

Does anyone know at what point the Oblivion Raiment item set is no longer viable or relevant?