I will only buy the magazines to find out what is new and upcoming. To understand what developments are happening and to make sure I am aware.
If you don't know what is out there especially in the technology field you will be left behind rather quickly. Basically i use it to keep up to date in whatever field I am interested in.
There are also some good promotions happening normally which I look out for getting an idea of what is a good and bad price for certain items.
I usually buy magazines related to technology, such as computer and linux magazines.
Things that concern me when buying a magazine are two. The first tutorial or tips about computers or linux. The second is about product reviews such as hardware and games.
The rest is usually only ads.