With the Rough Guides usual sense of humour, this is a fantastic book for a backpacker who is going for a short visit and does not want to carry a massive book.
In this book Rough Guides have trimmed the information back to the bare minimum. Please note this book is around half the size of the equivalent Lonely Planet guide for S E Asia on a shoestring - and if you want more info, get that book.
However if, like me, you are travelling in this part of the world for a few weeks only, and want to stay in many places and therefore only want to stay a couple of days, then this is a good book. Not too big to carry, this book has filtered out much of the lesser known places. The book has identified the main places where backpackers go to - and gives brief materials on where the main places to go are. Instead of giving a wide variety of choice, they have identified the MUST see sights. If you are like me - it is easier enough to fill in the gaps of this book by speaking with other travellers, going to agoda.com for hostels (lets face it - in SE Asia the listings in all the guides are never that up to date anyway!) and other travel agents and locals, then this is a great read. The book then serves as a guide to ensure you see coolest must see sights.
For example the bangkok section - if I did everything in the book I probably would run out of things to do after 2-3 days. The places mentioned frequently come up in travel tours like gap travels - so again if you want a rough ideas of what areas are covered - go to those websites.
Remember you can always pick up a guide in those countries itself where they are sold for a fraction of the price. However this rough guide can give you a good idea of what roughly you want to do overall.
If you are travelling for months rather than weeks, I'd recommend the lonely planet one which gives much more detail. (Or just buy the individual guides as well when you get to each country). But if you are travelling for a few weeks only - this guide is perfect as it's much smaller and much more compact, as well as being filled with the usual good advice.