I started adding serifs to my writing back in engineering school to help me decipher my own equations. I some moments where I couldn't figure out if I had written "+t" or "t+", or "is that a 2 or a z?!", and realized I had to create a script for myself and slow down a bit when writing.

Particularly troublesome characters that I remember were:

t vs +

u vs v

2 vs z

s vs 5

i (imaginary vs subscript marker)

g vs q (might seem silly, but prior to that, my handwriting didn't distinguish between them much)

o/O vs 0 (zero gets a slash, but never had situations where I was dealing with upper and lowercase o at the same time)

d vs ∂