Smart Cleaner App

No Apple does not recommend using any cleaner apps. The iPhone is very secure against viruses and hackers. It can get malware, but if you are careful about the sites you visit, you should have no problem...check this link...

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

A "cleaner app" will do nothing useful for your iPhone, but it will help to put money in the pockets of the folks selling this useless software.

No, you don't have yo use a cleaner app, it can make your phone very slow