The colder the freezer is, the faster meats, fish, shellfish will freeze, and the less the cell damage from growing ice crystals. I always freeze such thing unwrapped and in a single layer so they freeze as fast as possible, then wrap in plastic.

Things with salt in them are subject to rancidity because they aren't entirely frozen. Ham, for instance, is notorious for going rancid in regular freezer compartments. Lower temperature helps but may not cure.

Oily fish also goes rancid fairly quickly. Again, lower temperature may help.

Killing parasites in fish, -4F/-20C is recommended.