What's important to learn?
I find it is most important to learn and practice situations. This is why they have those premade settings in training mode--anti-air practice, Drive Impact practice, etc. e.g. isolated situations, which you practice recognizing and responding to.
Then there is integrating--practicing situations in isolation is excellent for training that procedural memory, but at the end of the day, we're here to play live unpredictable matches where many different situations are going to come out and combine in different ways. Sure, you can hit a counter Drive Impact in time--but can you do it under pressure with everything else about the match in your head?
But combos mean more damage and more wins, right?
In a word: exactly.
If your primary goal is to win more matches faster, yeah bud! Having delicious combos that you can deploy in the most common situations to secure those wins makes sense.
But my primary goal is long-term growth and mastery, and that means I want to maximize the situational practice I get from every match. I want to play matches that really test me on a lot of situations. I want to be recognizing and responding to as many different situations, as much of the time as possible.
Let's say you've got combos for days, and you can end a match by just capitalizing on three mistakes. All it takes is three mistakes - three punishable situations - for you to win. In other words: after winning only three situations, the match is over.
Without combos, it takes much more than three punishable situations for me to win a match. During the match, I could correctly read and win dozens of situations, resetting to neutral over and over--and maybe not even win! But I am in a stage of growth for the skill of playing these games, where getting practice winning a lot of varied situations is much more valuable than winning any one match quickly.
So when will you learn a combo?
Based on these ideas, the right time to learn a combo is when your awareness for a particular situation is so high that you are bored. If you are hitting opponents with your one-button anti-air every single time and you're sick of it? Now it has become valuable to maximize your punishment for that situation, because you no longer need to practice recognizing and responding--and it will add value to your matches by teaching your opponent they will get hurt badly if they do that, so ideally they will then stop doing that and give you more situations you haven't mastered yet. Either that, or you'll win =)
Defeat as a teacher
When committed to this model, you will come to embrace defeat as lighting the way. When someone shows you the holes in your game, suddenly it's extremely clear what situations you don't have an answer for yet. And you can just... go practice those!
If you've got a couple sick combos to pull out wins against the few situations you're good at, you might win a lot of matches instead of learning where your holes are. A win is a win, right? "Sure they almost had me, but I won in the end with my good combo, so I'm doing well." Be honest, what are you gonna remember better: the mistakes in the match you won? Or the mistakes in the match you almost won?
But I just want to win? I'm here to have fun, not get good at piano or whatever
Well, I am explicitly playing to get better at getting better at making music, so there ya go!