I don't use customize either, but there are very few things^1 that will be put in it without you
explicitly customizing the variable and choosing to save it. So rather than typing elisp code out by hand, you can use the more user-friendly interface to set a variable. If you're -- for example -- version controlling your init file and you use customize, you want to have your customize block version controlled.
[1] The only one I know about is `package-selected-variables`, which are "packages installed explicitly by user". It's used to make sure those packages are not considered unneeded if they aren't a dependency of anything.