Tablets are useful for commuters. If you're on a train you can read ebooks. Comics publishers now have tons of stuff you can read too. You can also watch Netflix and similar services that let you download content. This takes the edge off repetitive train journeys.

At work I've seen business analysts use it as a light weight laptop replacement to take notes (with the addition of the keyboard) and with the Apple Pencil to draw basic diagrams while on the go.

Photographers also use them to show off portfolios and do image editing editing on the go. You can get Lightroom and Photoshop for the iPad and other software vendors offer competing products to edit images on the go.

Also don't forget kids. For long car journeys, a tablet loaded up with a mix of shows and appropriate (often educational) apps can help them stop asking the dreaded "Are we nearly there yet?!"