Stylebook is my secret (ish) vice... takes quite a while to set up with pics of your clothes, and depending on the level of detail you go into with info about them, but once that's done it's easy to get into the habit of saving pics of the clothes you buy as you get them.
I use it daily to plan what to wear to work (I am not a morning person and haven't got the mental energy to think of what to wear first thing) and maintain wish lists/ check what I am and am not wearing a lot so easier to see what I should be getting rid of. Also use to plan packing lists (it's part of the enjoyment of anticipating a holiday for me now).
Initially I only used the "looks" function, but for the last few years I've been logging my outfits daily and that's the bit that tells you how much you're using something.
It's brilliant for outfit planning in particular - if I'm thinking of buying something new I use Stylebook to check it will go with enough things in my wardrobe. Stops me buying things that are too similar to what I already own. If I see someone in the street looking great, or a photo of an outfit I like, I'll put together something similar in the app or save the photo to the "inspiration" section for later.
It has helped me to refine my style, make sure I actually use my clothes and given me much more confidence with what I wear. I get lots of compliments on my clothes these days and I credit Stylebook for much of that, it's really changed the way I look at my wardrobe.
It is a bit addictive and sometimes too easy to justify a purchase just because it's on my wish list, but overall I love it and wouldn't be without it now!