Loosening the strings will reduce the tension on the neck, which might help when the case gets dropped or something. So, for that reason, it might be an arguable approach.
However, this business about temperature or pressure affecting the tension on the strings seems dubious. Wood has a thermal expansion coefficient in the range of 32 ppm/C to 42 ppm/C parallel to the grain. If I remember correctly, stainless steel has a value around 25 ppm/C. So, from that standpoint, the wood would get smaller faster than the steel elements (strings etc.) as the temperature drops - meaning the neck would get relatively shorter than the strings. That should tend to detune the strings, if anything; but, in any case, that is not a large difference in CTE. Pressure differences can only be 1 atm, so, that can't be much of a factor.
I personally don't detune at all, if a bass is going in baggage. I don't believe it would help much. If the gorillas are going to kill the bass, they will.
However, this business about temperature or pressure affecting the tension on the strings seems dubious. Wood has a thermal expansion coefficient in the range of 32 ppm/C to 42 ppm/C parallel to the grain. If I remember correctly, stainless steel has a value around 25 ppm/C. So, from that standpoint, the wood would get smaller faster than the steel elements (strings etc.) as the temperature drops - meaning the neck would get relatively shorter than the strings. That should tend to detune the strings, if anything; but, in any case, that is not a large difference in CTE. Pressure differences can only be 1 atm, so, that can't be much of a factor.
I personally don't detune at all, if a bass is going in baggage. I don't believe it would help much. If the gorillas are going to kill the bass, they will.

