How many ways are there to restore an iPhone?
There are two ways to restore an iPhone’s operating system. In both you need to physically have the device, but in one of them it can be done from the iPhone’s own settings, while in the other it is required to have a computer to connect it to. Visually, the process may seem the same, since in both cases the device data disappears and it is then asked to configure it as when it was taken out of the box the first time, but actually the internal process that has been carried out has not been the same.
From settings what you have to do is go to General> Reset and then click on «Delete content and settings». Once this is done, the phone’s security code and / or Apple ID password may be requested. If a Mac or Windows computer, you will have to connect the iPhone to it and open iTunes (on Windows and Mac with macOS Mojave and earlier) or Finder (Mac with macOS Catalina and later). Once this is done, click on “Restore iPhone” in the respective program.
Before iPhon can be backed upand, either in iCloud or by storing it on your computer. This copy can then be loaded onto the iPhone when configuring it, but it is not necessary to do it either if what you want is to delete all the data completely by not having the intention of wanting to recover it. Remember that there are also some data such as photos, calendars, notes and others that are synchronized with iCloud and will always be accessible.
Differences between these two processes
Well, when you restore from Settings what you are doing is overwrite data that you already had. It is true that once you have done the restoration you will not be able to find the data you had previously except those synchronized in iCloud or that you have loaded a backup, but for technical purposes they are still stored on the disk, only that the space they occupy can be occupied by new data when required. This method has the advantage of being faster than the other and that it can also be carried out in practically any circumstance, even if you do not have a Mac or Windows PC at hand.
However, for do a full format it is recommended to do it with a computer. Perhaps it can be more tedious, but it is the only way that exists to completely erase all the data that the phone has without leaving a trace of the previous ones. In fact it is the most recommended way to restore the iPhone if you want remove software bugs you were experiencing, although in this case it will be necessary that no backup copy is loaded, since this could bring back the problem.
Now, Is it always advisable to restore with a computer? Well yes and no. It is evident that it is a more complete and secure format in the sense that you will not leave data stored in the background that could cause problems, but it is true that if you need to restore for any reason other than software failures you should not have a problem doing it from the settings. In fact, this method is likely to be more practical if you don’t have a computer.