The Straight Leg Dead Lift is a variation of a regular Dead Lift -- but instead of generating power through your legs, you generate power through your hips and core. While it initially might look like a strain on your back, keeping a rigid back and using proper core and hip driving mechanics will make this work out build strength in your core faster than you can imagine.
The Straight Leg Dead Lift helps develop strength in your core, hips, and develops strength in the support muscles in your back. It'll keep you healthy, and injury free -- with an added bonus of teaching you proper lifting mechanics to avoid injuring your back in the future! This is a similar workout to many hip-thrust workouts that develop the abdominal muscles, hip joint muscles, and glutes. If you ever want to switch up your Dead Lift form, the Straight Leg variant is a great one to try!