E-mail usage for your device? I have a "serious" e-mail address that I use for human (to write and receive email from people that I really know) and another one as a nickname that I use in forums, registrations and so on when I use the PC.

At the serius e-mail address I have no SPAM, while in the second there is a lot of SPAM.

My Nexus4 is registered with the seriuos email address because I use a lot the e-mail on mobile.

Now many apps ask my email address to send me info, what e-mail do I have to set in the android apps? The device suggest me to use the seriuos one but I think that this choice can generate a lot of SPAM.
You can use any email you want to register for apps. Use the forum one to keep app spam off the serious one. Remember, purchased apps are still on the primary Google account, no matter what other address you register the app account with.