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Tidal torques play a key role in rotational dynamics of celestial bodies.They govern these bodies' tidal despinning, and also participate in the subtleprocess of entrapment of these bodies into spin-orbit resonances. This makestidal torques directly relevant to the studies of habitability of planets andtheir moons.  Our work begins with an explanation of how friction and lagging should bebuilt into the theory of bodily tides. Although much of this material can befound in various publications, a short but self-consistent summary on the topichas been lacking in the hitherto literature, and we are filling the gap.  After these preparations, we address a popular concise formula for the tidaltorque, which is often used in the literature, for planets or stars.We explainwhy the derivation of this expression, offered in the paper by Goldreich (1966;AJ 71, 1 - 7) and in the books by Kaula (1968, eqn. 4.5.29), and Murray &Dermott (1999, eqn. 4.159), implicitly sets the time lag to be frequencyindependent. Accordingly, the ensuing expression for the torque can be appliedonly to bodies having a very special (and very hypothetical) rheology whichmakes the time lag frequency independent, i.e, the same for all Fourier modesin the spectrum of tide. This expression for the torque should not be used forbodies of other rheologies. Specifically, the expression cannot be combinedwith an extra assertion of the geometric lag (or the phase lag) being constant,because at finite eccentricities the said assumption is incompatible with theconstant-time-lag condition.

Tidal Friction and Tidal Lagging. Applicability Limitations of a Popular Formula for the Tidal Torque