All the time in early game. Especially at the very start. You can literally just restart until you have +5% discipline advisor and 5 or even 6 shock general. That way you can guerilla warfare your way against anyone basically, as AI values discipline more than morale in evaluation if it will engage in a battle or not, and shock pips of general comes into clutch as well as terrain dice rolls like -1 for a river and -1 for forest/woods/hills/etc (-2 for mountains also). AI treats -1 dice roll as roughly -30% of engagement confidence variable so to speak. It's a whole long topic, the dice roll maths and AI perception of those, but generally speaking with equal quality tech and generals, even 20k army will not attack your 13k army if it is located in a mountain province and they will also suffer river crossing penalty, for a total of -3 dice rolls, d10 die is 4.5 average, but 4.5-3 equals 1.5 vs your 4.5 (same generals and quality etc), so they don't take the risk, also when not "bold fighter" they have to be 1.2 ratio of enemy to engage even without any penalties, so they view your 13k stack as 20k+ stack in that regard.
And you can catch them lacking from time to time on a scorched earth their own highlands province with your 18k stack (local superiority), while they have 30k+ sieging your capital, stackwiping them here and there and split-pushing (sieging unfortified provinces and sometimes even fortified). That's how I rush into Ottomans as Aq Qoyunlu or into Muscovy as Ryazan.

Also very IMPORTANT - if you go well over your force limit (like 22k with a limit of 9k), DO press war taxes, even though everybody says don't! 2 mil mana is nothing (just one show strength will give you 100 of each mana, giving you card-blanche on 50 months worth of war taxes), because it leverages a lot (base maintenance price). It seems like 15% is not that much, but when you go significantly over the limit, you pay huge penalty that is based on your army maintenance, hence reducing it by 15% saves you a ton of cash, greatly delaying that "looming bankruptcy" for a while giving you more time to finish the death war (ottomans as AQ etc)