It's mostly to do with musical grammar. Eg WhenFor example, as a crotchetgeneral rule, crotchets or a minim appears asminims shouldn't be placed on the 4th quaver of a 4/4 (and more so a 2/2) bar - as it does in your bar 12 - it hidesas they conceal the mid-point of the bar: makes it hard to see. Ties are needed.
[4/4 bars ARE often divided into eg. 3 + 2 + 3, but your left hand here is clearly in standard 4/4 or 2/2.]
I haven't done the expression marks, but you get the idea!