Yes, under specific conditions. If your goal is to theorycraft a speedrun, test a PvP build against a friend via TCP/IP (which D2R removed, but trainers can help recreate via mods), or you simply want to play a "Hall of fame" mode where you one-shot Diablo, then a trainer is essential.
No, if you value longevity. The magic of Diablo 2 is the unpredictable loot drop. The moment you use a trainer to spawn a "Tyrael's Might" armor, you eliminate the reason to play Hell Baal ever again. diablo 2 resurrected trainer offline
For the tech-savvy, Cheat Engine with a pre-made D2R table offers the most granular control. You can freeze monster AI, change rune drop rates to 100%, or modify the stats of a rare circlet directly in memory. Yes, under specific conditions
Instead of editing one item at a time, advanced trainers allow "item packs." You can spawn a full "Hammerdin Gear Pack" (Shako, HOTO, Enigma, Spirit, Mara's) with one click. The magic of Diablo 2 is the unpredictable loot drop