The distance you avoid by is related to height. Typical max distance required is 20 NM...this rule of 1NM / knot is serious overkill (and not practical in an unstable airmass where there are likely to be many CBs within 100nm). I think the original question may be asking about avoidance of Cu and other minor returns from the wx radar. If so the answer is again height dependent. At low levels in a relatively stable airmass there is no need to deviate around a little bit of green at low ranges...its just water! At 41,000 you wouldn't go anywhere near the same return....water has no right to be up that high. Ref also x band wx radar gain bias at short ranges. A small amount of cu (not towering cu) again is unlikely to give more than a few minor bumps at low level...can't complain if someone feels the need to deviate from it for pax comfort but it certainly does not deserve a delay to the approach. This lack of distinction between serious wx and slight nuisance stuff is most often seen in low experience aircrew.