What is the minimal seat post depth?
Most seat posts have a "minimum" insert of 3 to 4 inches.  But this varies with the material and the thickness of the post, and the weight of the rider means the minimum might still be too little.

As a tall rider I frequently have my seatposts up to maximum, and have bent several over time, and have fractured one frame.  Now I always buy a 450 mm or 500 mm post and almost always reinforce it with an insert tube up the middle.  I will not ride a seat post without 5" of frame insertion.

Since you sound like a MTB kind of rider, consider a dropper post rather than chopping ruthlessly through your seat poles with a hacksaw.  These are intended to go at a good height for normal efficient riding, but you can turn the interlock and they slide down ready for low-seat technical riding.  I understand you can do it one-handed while rolling too.

Once you're done you can raise the seat again without stopping.  Downside is they probably cost ten times more than a normal seatpost.