I also think steaks can be a good motivator, but it can be quite demotivating if you accidentally lose a long streak. That was the idea with the freezes, to still have the motivation element but try to cut out any of the annoyances that come with streak. They get automatically used, but as long as you complete at least one day before they run out, the number of freezes reset.
In terms of your situation when you had to travel, you could also pause the app. That way when you get back, you'd pick up right where you left off without losing anything. I don't think these ideas cover every scenario, so there may still be room for improvement
In terms of your situation when you had to travel, you could also pause the app. That way when you get back, you'd pick up right where you left off without losing anything. I don't think these ideas cover every scenario, so there may still be room for improvement