You asked

What is the nikon af s dx 17 55mm f 2 8g if ed good for?

Here is what the site says about that.

From Nikon AF-S DX 17-55mm f/2.8G IF-ED: Nikon AF-S DX 17-55mm f/2.8G IF-ED: A zoom lens by Nikon for APS-C cameras, 17-55mm f/2.8. Nikon's pro DX standard zoom: big and heavy. Specs - Maker: Nikon - Focal length: 17-55mm (zoom) - Maximum aperture: f/2.8 - Made for: APS-C sensors - Mounts: Nikon F - Stabilised: no - Autofocus: yes What it frames like - On APS-C (Nikon F): like 26-82mm on full frame; f/2.8 gives about the depth of field of f/4.2 there. ...

From Sensor sizes: The main sizes: - Full frame (36 x 24mm, the size of a 35mm film frame). The reference size: when people quote a focal length "in full-frame terms", this is what they mean. - APS-C (about 23 x 15mm). Crop factor about 1.5x (1.6x on Canon). Most entry and mid-range mirrorless cameras. - Micro Four Thirds (about 17 x 13mm). Crop factor 2x. Small, light systems from OM System and Panasonic. - 1-inch ...

Quoted from this site's pages.

From these pages