the practice of the scale focusing and aproximation...
do it first of all in your home. just for fun. take some object or be in some space and just guees what is the distance. then check it with your rangefinder if u r rite.
u will get used to the space where u maek the practice, but in other places u will not feel it anymore. that means again, practice. at some point u will allways feel the distance.
now about so called tolarance of this focusing. it is never supposed to be the most accurate. but the u have the natural depth of field of your lense. that means that in order to be confident u have to be in the tolarance range of about f4 on the normal lense, which means that u can practically use the f8 for serious work etc.
the tolarance is: since u cannot be perfectly accurate u still can make focused image because of depth of field. if u have this mistakes - the depth of field compansate for it. but the more accurate u are the better for u. u can use wider opening.
then of course u will be expirieanced wit hit and u will know very well how to place the focusing since u will know to sense the distances of the object and what u want to be in focus and what not.
i know that it sounds complicated but, but with practice it gets much eassier and the most useful thing (u cannot even imagine how much) in all those situations that because of focusing u loose the moments. u will feel very free and very intuitive if u will master yourself in this way.
of course when there is possibility to focus perfectly accuratly, u should focus the normal way.
for longer than normal lense this way of focusing is not practical, while with wider lense like 35 or 24 etc u will feel even more confident than with the normal lense.