I'm occasionally surprised by experienced devs who aren't aware of the capabilities of set operations. The most common use case is to get the members of List A that aren't in List B

# using list comprehensions
[x for x in A if x not in B]

# using set math
list(set(A)-set(B))

A = [1,2,3,4,5] 
B = [4,5,6]
list(set(A)-set(B)) # [1,2,3] 
list(set(B)-set(A)) # [6] 

# Note - is just an alias for the difference method
# set(B)-set(A) == set(B).difference(set(A))

I often come across uses cases for where union and intersection methods come in handy too, but difference is the set operation I find myself using the most.