If you get Windows Azure subscription, there is a Spending limit on it. But turning it of made it impossible to add it again later. That pretty annoying especially for the starting Windows Azure developer to keep the costs down. If you connect your Windows Azure subscription to your MSDN account, you get credits to use for every resource on the Windows Azure platform.
Even then you want a limit to the costs beyond the credits. Nowadays you can put the spending limit on, but it is all or nothing.
You would rather set an alert if you reach a certain amount. You want an e-mail, so you can go to the portal to remove/shutdown or close unnecessary instances.
This is preview option. You can set an alert on total amount or available credits!
This makes it much more relax to connect your Windows Azure subscription to your MSDN account. This way the costs are manageable.
Happy Cloud developing!