for one, anything done more easily in portrait mode vs landscape, most especially web browsing and e-reading.
here's a bunch more reasons and uses
- lighter and more portable by far
- significantly longer battery life than even a netbook
- still gets alerts and notices even when in sleep mode
- hang from the seat in a car for on-the-go video entertainment
- more comfortable to use laying on a couch
- if you already also have a desktop PC, no second full PC OS to care for (patch, maintain, secure, update) and buy expensive app licenses for. Having both a desktop and a laptop/netbook is kind of dumb, and performance laptops are more expensive than a desktop and a tablet combined.
- thousands of great apps under $5, not starting around $50.
- easily used while standing
- can handle levels of 3D gaming only notebooks costing 2+ times the price can meet.
- easy to enable parental controls
- 3G Data plans from $14.99 up to $30, not $60 for aircards or relying on MiFi's with 4 hour max battery life.
- no contract data plans
- remote wipe if lost
- has GPS
- UI is very easy to use, and apps customized to be used by fingers on appropriate screens (does not yet apply to Android)
- great for kids you don't want to give a full performance laptop to.
- easy backups without 3rd party software
- counts as a personal mobile device for insurance purposes (laptops typically require rider policies to be covered by car insurance, but many other devices like phones and cameras do not require one, or come with lower premiums, depends on insurance company).
- easier to gain HIPAA and SoX and DOD STIG compliance for companies
- no spinning disks
- you can find a charger almost anywhere in a pinch, worst case buy one for $10
- easily powered by cigarette lighter sockets
- easy to sync with another machine and/or the cloud
- resale value still at higher than 50% after a year,as high as 75% common
If you have a notebook you're happy with, and don't mind lugging around, and a smartphone that can already tether, there's certainly fewer compelling reasons to add a tablet to the mix. Personally, I'm planning on getting an iPad 2 (if Android 3 fails to impress, I'm not too happy about the descriptions of their "panes" model of their tablet OS screen use), and honestly, it probably will rarely leave the house except on vacations, I'll watch TV and read books on the couch while watching the kids while the wife watches boring crap or kids shows that make my ears hurt.