In reply to Ramblin dave: Body tension means your postural muscles are able to keep your body in certain and at times very difficult position without. It means your body core is able to provide support to your limbs, so they can generate enough leverage.
If you forget for a while about climbing and footwork techniques, egyptians, flags, twists, etc. and you hit on a steep wall keeping your position open, then you will understand role of body tension.
The mighty Malcolm Smith may well help to understand it too
The keywords are: stay open, long and big moves, front to the panel/rock, bad footholds.
Climbing problems on sloppers are quite specific in such way applying the masterclass'y footwork technique may be impossible, then body tension generated by the postural muscles is the key.