Clearbit will take a very basic set of information like an email address on a Contact or a website on an Account, and deeply enrich those records with all sorts of useful data.
Best/Cleanest UI among data tools. Easy integration. Tons of useful things like chrome extensions, widgets, etc. Having rich data helps you uncover all sorts of previously unknown insights.
They "only sell to clients with a global Alexa score greater than 100K", and won't respond to lead forms or allow self signup for anyone else, which is infuriating. I've personally recommended Clearbit to a big client of mine and then installed it into their org, only to have Clearbit completely ice us and make me look terrible. 0/10 would not recommend ever again. Also, incredibly expensive. Long term lock in Contracts. Mostly an all or nothing service for Sales teams with a budget for data that exceeds 5 figures per year.