Vital! I posted on this probably 2 years ago. I have not been actively using the snap technique and still have depression. But I found that when I DO use the snapping, I instantly remind myself that I am here. The reason why the snap technique works is because you're in the PRESENT. I know you've mentioned this before. I find that people with depression constantly have their mind wandering about other things- whether that be worrying about what others are thinking of you, worrying about consequences, thinking about existential questions, thinking about things that are bothering you, constantly finding solutions to fix your mood, etc. People who have depression aren't in the present like those who don't suffer through depression. The sadness is always lingering throughout and we're always thinking about it.
The snapping technique works. I am going to share this with others. Thank you for this again.

Another thing I'd like to add is that focusing so much on unanswered questions, depression, the pain of depression just makes your attention focused on that and only that. So it is best to be active, be productive, keep yourself busy doing things you love because that is also a way of staying in the PRESENT. It's all about staying in the moment and not having the depressive thoughts on your mind.