I refer to the gluteals as the body’s “engine room”.
The glutes produce the power you need on the bike & run, and provide stability during the swim.
If you’re not sufficiently engaging your glutes, then you’re probably overloading your hamstrings and quads.  Have you ever been reduced to walking or have suffered cramps on the run during a race?  If so, then your glutes probably need some work.
Endurance athletes — at all levels — typically have notoriously weak glutes.  Even many pros who I’ve coached displayed significant imbalances in their gluteal strength.
Check out this video… It introduces a simple routine you can do anywhere (in the gym, while traveling, or at home) that will increase the power in your “engine room” in no time.