Apart from giving you a legal high the deadlift is good for straightening out and giving you a trunk of steel on moves but impressive as it is (see below) as a climber if I was allowed only one exercise it would undoubtedly be pullups on a fingerboard.
From wikipedia
The deadlift is a compound movement that works a variety of muscles groups:
The grip strength (finger flexors) and the lower back (erector spinae) work isometrically to keep the bar held in the hands and to keep the spine from rounding. The gluteus maximus and hamstrings work to extend the hip joint.
The quadriceps work to extend the knee joint. The adductor magnus works to stabilize the legs.
The deadlift activates a large number of individual muscles:
Torso
Front
Abdomen
Rectus abdominis (under aponeurosis)
Abdominal external oblique muscle
Abdominal internal oblique muscle
Back
Iliocostalis
Intertransversarii laterales lumborum
Latissimus dorsi
Levator scapulae
Longissimus
Quadratus lumborum
Rhomboideus major
Serratus posterior superior
Serratus posterior inferior
Splenius cervicis
Teres Major
Trapezius muscle
Legs
Quadriceps
Rectus femoris
Vastus lateralis
Vastus intermedius
Vastus medialis
Hamstrings
Biceps femoris muscle
long head
short head
Semitendinosus
Semimembranosus
Hips
Gluteal muscles
Gluteus maximus
Gluteus minimus
Piriformis
Superior gemellus
Forearms
Flexor digitorum profundus
Post edited at 10:41