Extremely easy to use, lets the user programme a great variety of actions.
The only thing the app needs is a "trigger" (representing some kind of event) and then it automatically starts whatever action the user coupled with that event. The system is absolutely functional and easy.
Regarding the Android app, which I used, I cannot do anything other than praising the dev team for the good job: no issues whatsoever during my testing (and curretn using) and I find it very complete, I don't feel like I need to go back to the website to do anything.
It might not be that attractive to people who are not interested in technology. Plus, advanced settings can be a bit easy to set for the same users (they can be left as default, anyway).
Just let the app give you a few examples of what you can do and connect all the services you already use: it's impossible not to find something that can automatise a process you're doing manually.
IFTTT let me automatise a series of actions with literally a couple of taps on my smartphone screen: considering the large number of services it can link to (Facebook, Twitter, Instagram, LinkedIn and GMail just to name a few well-known ones), there is really plenty of room for everyone to create new "recipes".
Personally, I found a helpful one straightaway: I use both Dropbox and Google Drive and I like them to be synced so to have the same files in them both: one quick rule create and I solved the matter, I don't have to do it manually anymore.
But it's really a service capable of interacting with many others, so one example does not make full justice of how much it can be valuable.