Cold-Blooded is rather versatile, as any weapon or play style can benefit from not being tracked. However, it reaches its full potential when used with a stealthy and mobile weapon, such as the Carbon Roller or Octobrush as it can enhance the sneakiness of a weapon, facilitating ambushes. A loud or otherwise conspicuous weapon may give itself away to surrounding enemies, no tracking needed.
In Splatoon 2, Cold-Blooded was a stackable ability that was available on any gear type. It could stop the tracking effects of Point Sensors, Ink Mines, Thermal Ink, Haunt, and the Sting Ray.
In version 4.3.0, Cold-Blooded was retired, and its effects got combined with Bomb Defense Up to make a new ability: Bomb Defense Up DX. The default ability of all gear with Cold-Blooded (except the Gray FA-11 Bomber, Pearlescent Crown and Fringed Loafers) was changed to Main Power Up, while existing gear with the Cold-Blooded ability was overwritten with Bomb Defense Up DX.
▲ Preexisting mains changed to Bomb Defense Up DX.
— Items originally with Cold-Blooded as a main can be repurchased with Main Power Up (aside from gear unobtainable from SplatNet 2, which have Bomb Defense Up DX).
▲ Preexisting subs, ability chunks, and drink tickets changed to Bomb Defense Up DX.
Trivia
In Splatoon 2, Cold-Blooded was the only ability that was favored by two brands.
In real life, all squids are ectothermic, or "cold-blooded", which the Cold-Blooded ability could be a reference to.