Well if you did not got your hands on the first generation Nexus 7 , i.e., the Nexus that was launched back in 2012, you have at least heard of the performance issues it had. Although the Tablet was brilliant the moment it was launched, but the quality and performance degraded over the course of time, and in about one year it started getting some complaints.
What is TRIM ?
When you delete any content off the memory, the data is not removed but the device shows it is. And when you transfer any data again it simply overwrites on the existing data instead of using up the fresh memory blocks. So this thing really degrades the performance of the tablet as overwriting on the existing data takes up more time then the writing up on fresh memory locations. And this is the only thing that the new update fixes up in the older Nexus 7.
So just hang on a bit and try the Android 4.3 update to get things back on track for your old Nexus 7. Are you enjoying Android 4.3 on Old Nexus 7?