I use my own domain, so I can do things like Home Depot, At my domain, and Amazon at my domain, and eBay at my domain, etc. So if anybody besides them emails me, I know that it has been misused or lost.
Some websites don't recognize the plus trick and won't accept it. And I use my own domain so that if I wish to switch email providers ever again, I don't have to switch all of my email addresses again. I can just switch my domain to a new provider and all of my emails stay the way they are.
Lots reject it. Most retailers use emails like phone numbers: unique to a single person. They often simply reject temporary emails of this nature. In fact, at one point even lemmy.world was not signing anyone up if they used temp emails.
Which is another reason that I don't use temp emails and use my own domain instead. I have run across that once or twice when using aliases like simple login.