Once you can visualise what’s going on in plant it can help a lot
Think of the roots as a pump
They send the fluid up plant building up the presure within the plant starting at the most important part the top and then as presure builds the buildup graduallay works it’s way down plant
So overwatering is plants start curling fans / leafs at very top first and then as presure builds further , curling progresses down plant
( curling is witch fingers , cuz too much heavy fluid in leafs making them curl and hang low )
Underwatering , plant will lose pressure at bottom of plant first bottom fan stems will not have the turgur to hold them up and then fans will wilt too and as presure keeps decreasing , floppyness will move up plant
Once you visualise that , think
How would removing roots affect that system
And at the other end of scale , what does defoliation do and how does that affect system
and what will this affect then lead too ( like say ppm of nutes needed )
Etc etc