> If you're working with sets of 10 items
If you are working with a hardcoded 10 items, and you are certain that won't change significantly, sure.
If not I strongly disagree, because I've seen way too often such cases blow up due to circumstances changing.
Now, if it is very difficult to avoid a nested loop then we can discuss.
But it can simply be due to being unaware that some indexed library call is in fact O(n) or something like that, and avoiding it by using a dictionary or some other approach is not hard.
While constants matter to some degree, the point of big-O is that they don't so much if you get handed two orders of magnitude more data than you expected.
I'll gladly sacrifice a tiny bit of performance for code that doesn't suddenly result in the user not being able to use the application.