Purpose of Image Capture app on iMac

Image Capture User Guide for Mac - Apple Support

Used for accessing and downloading images from USB-connected iPhones and iPads. Perhaps some supported cameras too. Image Capture will transfer the files to the Mac and use the image's internal EXIF DateTimeOriginal metadata to set the creation and modification date of the images. It allows you to add those images to Apple's Photos application too. Without Image Capture, simply dragging and dropping images from the connected device uses the current operating system date/time stamp for creation and modification dates.

Image Capture can drive selected scanners including a few USB devices supported by Apple's built-in AirPrint (e.g. Canon LIDE 300/400). Some vendors issue an ICA-named driver for specific Image Capture support of their scanners and that driver needs to be compatible and installed with the current operating system.

The third-party Hamrick offers paid, robust scanning software (VueScan Professional) for about 7400 scanners. Many of those are supported without any vendor software or driver requirements, though some scanners do require vendor drivers as a prerequisite installation. Hamrick gives that detail for each supported scanner.

I use Image Capture to Scan from my all-in-one Printers instead of the manufacturers scan-ware.

Scan images in Image Capture on Mac - Apple Support

Not so much any more, but in the old days I used it to Transfer pic's and movies from camera's to Mac's.

Transfer images in Image Capture on Mac - Apple Support

I use it to scan documents from my HP Printer. It is also used to import photos and videos from a camera.