You are actually just putting the data on it marked as "free space" but not really deleting it.
Beware that may be possible to recover your data on it if did that way.
The often called "full format" usually requires more time because it will erase all your data and overwrite your data with zeros and also scan the hard drive for erros and bad sectors.
Prior to Windows Vista the "full format" does not write zeros on your data so you might consider an 3d party program for that.(edited to adress what @Daniel said on comments)
It's usually the safest and preferably option if time isn't a problem or you need to make sure nobody can recover your data.
Regarding the above risks there is no difference. With every format the operating system writes the file system structure, and this structure is the starting point for every file system access. It does not make any difference if unused sectors are zeroed out or filled with random data.