Why we write the line -" max_index = len(words) - 1" in the program given bellow?

Question

words=["hello", "world", "spam", "eggs" ]
counter =0
max_index=len(words)-1

while counter <= max_index:
word=words[counter]
counter=counter+1

Answer 1

Because indexing starts from 0 so in words
0 refers to Hello and 3 refers to eggs
And length function counts the number of items like there are 4 in it and returns the value
And obviously there isn't anything at index 4 in words

You could even do
while counter<len(words)

Answer 2

Just to make it clear that maximum index in the list is 3
max_index=Len(words)-1 means max_index=3
Much readable than just doing
Counter<Len(words)

Answer 3

Why we subtract 1 from "len(words)" ?