Ohhhh ... I like that model! I'll have to remember it!
When someone comes to me and asks me to architect a solution for them, they're basically saying, "we've got this great idea and we need to turn it into a living breathing thing. Can you help us?"
In other words, they want me to breathe life into their idea. Without it, the idea isn't worth the paper it's scribbled on.
If I succeed at breathing life into your idea, I want to be compensated for that beyond my hourly wage. Why? Because I want to participate in the VALUE I'm CREATING FOR YOU.
Put another way, I need to be smart enough to question a bunch of stuff and not just blindly build whatever you think you want wherever you want it. Imagine building a huge glassy office park in the middle of a slum, and you cannot get anybody to rent space in it. Why is it in that location? Because I didn't question you when you said that's where you wanted it built. Maybe it's because I'm from another city and didn't know it's a slum. Maybe I just don't want to "rock the boat" and disagree with you. Whatever the reason, if I build it and you cannot monetize it, then we both lose out.
I have a vested interest in your success by having equity in addition to my regular fee. You don't want a "yes-man". You want to build a successful business. Sometimes we may be at odds. But if you know that I've got a stake in the outcome, you might just pay attention to what I've got to say instead of sticking to what your over-bloated ego is saying sometimes.
Equity for the architects/designers of tech stuff keeps things in balance.
Cashflow ... same thing. It's icing on the cake.
I can also say from experience, most of the time that equity will never be worth a penny. Which is why I also won't work for 100% equity -- if it's your business, and you have a controlling interest, then the rest of us are essentially along for the ride. People who don't realize that probably aren't reliable themselves, and will bail as soon as they hit a financial bump personally.