Running out of space on your Gmail, now instead of having 10 GB storage for Gmail and another 5 GB storage for Drive and Google+ Photos, Google will be offering 15 GB of unified shared storage for free between Drive, Gmail, and Google+ Photos.
With this shared storage, users can use this storage how they need to. If you are a Gmail addict and end up with lots of emails and attachments, all the Google Drive and Google+ photos storage capacity will apply to your Gmail storage leaving you with lots of additional storage option for your mails. Similarly if you are photographer and shares your photos to Google+ then all the storage capacity from Gmail and Google Drive can be used with Google+ Photos.
In addition you can also purchase additional storage space that can be shared and used between Gmail, Google Drive and Google+ photos. Plans range from $2.49 per month for 25GB to $799.99 per month for 16TB.
Also according to Google Enterprise blog, Google Apps business customers are also benefited by this change, they can now get 30 GB of unified storage between Gmail and Drive. Storage will also be shared with photos you upload to Google+ larger than 2048px.
These changes to storage will be rolling out slowly over the next couple of weeks, so you may not see this changes applied to your account immediately.