Years ago I had a blog at this same domain, jacobmckinney.com. I did a bunch of on-page SEO and had several other sites linking back to mine, so I had a good bit of traffic. My content was centered around topics geared toward small business owners. I eventually abandoned my blog (don't do that) and let my domain expire (don't EVER do that, seriously).
So what happens when you let your domain expire?Initially, the domain moves to Registrar Hold status for up to 45 days. After this 45 day period, the domain moves to RGP (Redemption Grace Period) status for the next 30 days, the cost to renew the domain also (generally) goes up at this point. During both the Hold and RGP periods DNS, web services, and email all cease to work for the domain.
After this, the domain can no longer be renewed and goes into a Pending Delete stage for up to 5 days. Once the registrar decides to delete the domain, it is dropped and available to be registered by a new owner.
Often, once a domain with any amount of real traffic is dropped it is often immediately picked up by someone who wants to use it for evil (either hoping you'll pay a ransom to get it back or looking to exploit that traffic).
This is exactly what happened to me.
I let my domain expire and someone bought it the same day and put up an e-commerce site in Japanese.
"But wait, isn't this jacobmckinney.com that I'm reading right now!?!?"
Yes, yes it is.
I had to watch my domain (with my name) for two years before it became available again. In the meantime I was forced to use other domains for my projects (jacobmc.com). Eventually those who bought it made the same mistake I did and I was able to register my domain again.
So long story short, don't let your domain expire, even if you think you won't be using it for a while. Trust me, it's much easier to pay a few dollars to renew your domain than having to wait years to get it back. I was lucky, some people don't ever get their domains back, or they have to pay ridiculous prices to buy it back from someone.
So renew your domains, always.