Most lower end heatspreaders are absolute crap and have no surface area (see Viper Steels), probably would do about the same thermally without them. Honestly I'm not even aware of any DDR4 heatspreader that actually looks like it has impressive surface area. Trident Z could be okay if it didn't have that plastic piece/stupid RGB diffuser on top - I removed the plastic piece on my E-die Tridents but for the RGB/Neo/Royals you can't just take off the diffuser. I took the heatspreaders off my 4133CL19 Viper Steels for clearance, they've been running naked fine at 4200 17-18-18 1.45V for a while now.
It's really only a specific subset of DDR4 that might benefit. Within DDR4 there are only a few ICs that can safely handle 1.5V or more > within those there are only a few that can do tight timings (B-die) or high freq (Rev.B, DJR) > within those there are a few that are temp sensitive and destabilize at x temp so actually need the cooling. DJR comes with crazy factory XMP up to 1.65V.
Mostly it's airflow that matters much more than what heatspreader is on there. Heatspreaders with poor airflow are useless, but not vice versa. I'm not so sure about dual rank sticks, a heatsink might knock off a few degrees (again, not just any old dual rank 3200CL16, but dual rank B-die/Rev.E/(Rev.B?)/(DJR?) @ 1.5V+).
But then again, people love parroting the idea that watercooling RAM is useless, but a properly put-together waterblock setup can actually be beneficial for a B-die daily system pushing 1.55-1.6V (say, 4000CL14 on Zen3, 4600CL16 on CML etc). Especially with a 200W+ GPU in the system dumping heat onto the DIMMs.
