Mobile proxies are addresses from cellular operators. Their main advantage: they look like real users on real phones. Sites find them harder to detect, so mobile proxies get banned less.
But there are downsides: they cost more and are slower than server ones. For most tasks plain datacenter proxies are enough. Mobile ones are needed where anti-bot is especially strict: ad arbitrage, mailings, some social networks.
If you buy mobile proxies, look at operators and countries. For scraping from mobile addresses, a refreshing pool matters too.