CompatibilityLevel in Sharepoint 2013

Hello,
I have few queries around SharePoint 2013 14/15 Folders.

I created two site collection on SharePoint 2013 environment:-
First in SharePoint 2010 Mode
Second in SharePoint 2013 Mode

Now i deployed a simple wsp solution(Site Collection Scoped) using powershell script.Since in the manifest file,the solution was targeting 14 folder,as expected the files related to wsp solutions were deployed to 14 folder.

My assumption was that the feature in a solution will only be avialable on site collection in 2010 mode.
However it was also avaialable in Site Collection in 2013 mode.

If that is the case,what is the use of Compatibilitylevel parameter during -Install-Spsolution command.