what are good things by using an operating system on a flash drive

Some of the reasons why booting an operating system on a flash drive or cd is good because theres no logs and you cant save anything on the operating system so others dont know what your doing on it if you playing games. Another reason is because you can try an operating system that you dont know if you like or not and just not have to install it you can try it out. Also you dont need a hard drive to install an operating system because if boots from the flash drive/cd and if you dont have one you can still run an operating system and go online. A reason why its not a good idea is because it might go slower and you might have to buy a bigger flash drive to fit the operating system on it. Another reason why its a bad idea to do is because you cant save anything if you dont have a hard drive. Thats the good and bad about running an OS on a flash drive or cd