It’s basically a universal way to transport additional user info or data between different environments/platforms without storing it somewhere in cookies.

It’s most commonly used for marketing purposes. These parameters/tags can be recognized by analytics software to collect relevant data about their page visits. E.g. it will allow them to analyze how the visitors arrived on their website, which search engine or advertisement did they come from, by which keywords, etc.

Another common way they’re used is for usability aspects by the website itself. When a page loads it will read the tags for user preferences like search order, filter options, interface settings, etc.

It’s basically harmless, the data isn’t as personal as cookie info. There’s no harm removing it from the url to make it prettier, but leaving it there doesn’t hurt either.