Update from OS 10.7.5
What are the cons of upgrading from iOS 10.7.5 to Yosemite?
iMac, Mac OS X (10.7.5)
iOS is the iPhone, iPad mobile platform
OS X is the computer platform, soon to be MacOS with the release of Sierra 10.12.0
There is no benefit in getting too far behind in the OS or in the technology—just makes it more difficult to successfully and smoothly insure a smooth transfer of all your apps/data/iTunes/Photos etc
The latest OS is always the most up-to-date security wise.
You do not specify what machine model/year amount of RAM or any pertinent details,
see this ref: OS X Yosemite - Technical Specifications
The biggest con in upgrading to Yosemite is when MacOS Sierra is released within the next couple months you are still 2 operating systems behind.
