How do you use zip files?

Question

Hello all,
I have always stayed away from ZIP files (as in doing it myself, to my own files), since my days in Windows, after all the countless corrupt ZIP files I received from others, that simply would not UNzip...
But recently I've come across references to them again, and I realised I might be missing a trick or two....
Any comments on the following would be appreciated:
1.) What can I use them for?
As in - could I ZIP my entire folder of holiday pictures - all 13GB's of them?
Or is there some sort of size limit, where anything over, and things become problematic?
Are some file types Zipped better than others?
2.) How does it actually work?
As in - what happens to my original files?
Assume the holiday pics are Zipped - do the orginals get compressed, or can I select it so that copies are Zipped, as a kind of backup?
3.) How safe is it?
As in - assuming my hardware and software are all OK, nothing buggy etc. - if I create the ZIP file, pop it somewhere on a USB/External/the same laptop, and then Unzip it later, when I need them again - am I correct in assuming that the chances of the file being corrupted, are relatively slim?
And coming back to those holiday pics - could the compression process result in a loss in picture quality/resolution, were I to then unzip the file? Or - assuming everything works as planned - will the quality of the pictures/file emerge exactly the same as they were prior to being compressed?
I realise all of the above are ridiculously simple questions - but googling this doesn't really help, as most sites simply explain the how to, not the WHY...
The WHY articles were probably all written 15 years ago already... I'm just very, very far behind....
Thanks in advance!
[Mid-2012 MBP 8GB Ram; OSX ML]

Answer 1

Zipping an image file should have no effect on image quality, as the image data is not actually changed.
Note that there's very little point in zipping a folder full of images, unless the images are not a compressed file type. You can't compress data that is already compressed - in fact, trying to do so often increases the file size - and JPEG images, for example, are already compressed.
For the most part, you don't need to use zip at all. I absolutely DO NOT recommend storing your files and/or folders on the hard drive in compressed form as a space-saving measure. It doesn't save enough space to be worth the time needed to compress files large enough to warrant it on a modern drive. Accessing zipped files is a pain, too, since you basically have to decompress the whole thing in order to access a file inside a zip file.
Zip becomes useful if you need to attach a large number of files to an e-mail message (zip the files, then attach the single zip file) or want to create an archive of multiple files to download from a web site through a single link. In other words, in situations where you need to transmit many files over the internet, especially where Windows users may be involved, zipping files can be either important or a convenience.