When you self publish an e-book, you need to figure out on which platform to publish, different platforms take different cuts in your revenues but also give your potential readers a choice where to purchase from. Some may not mind buying from your personal site, but others only buy from established online stores.
At the start of things, I just published on Gumroad because I was still writing the book and looked for the simplest solution that would allow me to have pre orders, plus I wasn't even sure if anyone would be interested reading my book!
When I launched I also published on Amazon, since I it's the biggest online book store, and it gives credibility to your book, if you appear there.
After launch I got accepted into Appsumo's marketplace which was overall a nice experience and offered some exposure to the sumo community.
Sometime after launch I decided to drop Gumroad and focus only on Amazon and Appsumo, and recently decided to give KDP Select a shot, which means I had to drop my product off Appsumo.
For those who don't know what's KDP Select - it's a program where you make your book exclusive to Kindle and get access to Kindle Unlimited.
You can check out my book Start with A Side-Project on Amazon and let me know what you think of it.
Will see how this move rolls out!
Cheers