This is great news for user of blogspot.com or blogger.com. It is even easier and more flexible with this new function. There is some limitation that you could only have Google Adsense for the inline advertisements and some of the old customized templates will not work with this, you may have to consider newer templates.
But you did not pay for hosting or the domain, therefore everything you earn from Adsense or any advertisements program is pure profit (deducting your own time & pay).
To learn how you could show adsense between post.
[...] of blogspot owner are starting to have adsense but my advise is always have you domain. Although blogspot allows adsense, it is always good to carry your own identity rather than carrying blogspot [...]