Here we get a 5 gallon bottle (if it fits) inside the piano. It is believed that it keeps the humidity stable in the Piano.
Keep in mind that this is super dry, desert dry climate.
What do you think of it?
I do it sometimes and sometimes I don't. It depends on the piano.
Some pianos are good dryer because when humidity kicks in after 100 years of dryiness hammers or keys get swollen and stuck.
Is it good logic or not?
Yes, I have heard of this method and have found a number of jars inside upright pianos (usually empty because the owner forgot or someone else put it there). I think they are certainly helpful, but water only evaporates so fast, so effectiveness is minimal.
William Braid White mentions this in his book (see photo).
I agree that adding too much humidity too quickly to old wood can be problematic. I always suggest 40%-50% for hygrometer readings near a piano. 
