I have never thought I will buy single app to optimise JPEG files. And honestly – this is the best spent less then 20 USD in 2014 for any app I have bought.
JPEGmini does only one thing: recompressing the JPEG files. You can use it also to scale down images, but – my use of this app is optimising JPEG files for blog/publishing but also for my Clients backups. JPEG export is build in most of photo editing apps however – I was not happy with use of Image Processor (Adobe Photoshop’s part) nor Adobe Lightroom – because of handling of compression. So – while JPEGmini keeps details and quality of it’s processing – I’m happy. How much space we will save? I think 2-2,5x is average what we can expect and what is real to get. With not visible loosing quality of our images – a great deal to go with.
So – this is my recommendation wherever you are photographer or just blogger or hobbyist sending pictures to family or friends.
PS. there is also Windows version of JPEGmini.