To be fair, if a noob comes here from playing Risk then attacking a larger stack with a smaller one is a legit tactic. It took me a while when I first started playing before I understood that Warlight uses a different mechanic entirely for battles, which mean that you need to attack with more than the defender else it's bad. There's quite a few things like this that a really good Risk player will get wrong.
Dunno if attacking territories with less armies can ever be good in risk lol, it's really a last hope tactic and you depend entirely on luck to win. I really avoid attacking on risk unless I have the absolute certainty that I'm conquering a province, or else it's a waste of armies.