When you signup at USCIS website, you can enroll for email or text messages updates so USCIS site will send you message as and when there are any changes.
I thinks soft update means there are some updates that would generate status change on website and send email/text but no paper mails for eg. "In Q 4 Interview Scheduling", "In Q 4 Oath Scheduling" whereas hard update means a paper mail would follow for eg. "Now you are scheduled for Interview and you would receive notice in mail", "Now you are scheduled for Oath...."
It is my understanding and in my opinion, I wouldn't worry about all technicalities unless I don't see any updates for 2 months. In general, for best case scenario, it would be over in 3-4 months whereas worst case scenario would take 6-8 months" so don't worry much about it.