This may be to make them better fit into a document or email, or to used resized images on webpages or they can be used to be set as a wallpaper on your desktop, or for many other purposes. There are many reasons to resize pictures or photos on a Mac.
The application has been made like a wizard where you can apply several editing functions to a batch of images.
Photos Resizer is a lightweight app to resize images in a batch.
Test it out as Free version allows you to resize 15 Photos for Free. Photos Resizer is a Batch Image Resizer to quickly resize, rotate, flip or rename images in a batch.