While you using your pc, it keeps saving data as temp, cache and history and also registry for the programs you setup and a lot of other many files that make your Windows slower and may be it wouldn’t be able to start, so if you wanna save you windows to be fast and work properly for long time you must use program clean all of this for you.
CCleaner one of the most free programs now, it uses by millions worldwide, it clean your p to be like new.
it also has many options make you keep your passwords or history if you need them and also you an clean your registry with few clicks