Modifying a list while iterating over it with a for loop can lead to unexpected behavior or errors because the list's size changes during the loop. For example, if you try to remove items from a list while looping through it, some elements may be skipped or not processed as intended. A better approach is to iterate over a copy of the list using my_list[:], or use a list comprehension to build a new list based on a condition. For instance, instead of removing even numbers with a loop, you can write my_list = [x for x in my_list if x % 2 != 0]. This keeps the loop safe and ensures the list is modified correctly. Alternatively, the filter() function can also be used to achieve similar results in a clean and efficient way.