On one projects, my softsynths started displaying latency.  The behavior was odd: if I reset anything (e.g. turn recording on and off) the latency would go away, but as soon as I pressed "play," it would come back.  Some detective work revealed that it was the number of plugins I was using that was causing it: when I disabled them, the problem went away.
   Now here's the puzzler: my I7 CPU meters were barely budging.  So, I was hoping someone more technically minded than me could explain how the plugins were bogging down the machine even when the CPU (and ram) were not showing any overload? 
Thanks!

Some plugin effects have buffers in them. These effects are not meant for recording, they are meant to be used for mixing.
 
CJ

Yup - some plugins either use look-ahead processing, or or otherwise CPU-intensive, and meant for mixing/mastering, not for tracking.
 
The general approach lots of folks take is during tracking to swap out the latency-inducing plugins with other less demanding ones, then after done with tracking put the real 'meat and potatoes' plugins back in, adjusting settings as needed at that point.
 
Bob Bone
 

I had a TRANSIENT plugin on my kick which caused latency.  Removing it took away all the latency...

I wish Cakeland would have a sticky ion what plugins have these kind of buffers that make it non useable for recording as this question gets asked way too much.

Well, I had a transient plugin on my kick too, so I will check to see whether that was the main culprit.  I still don't understand my original question:  If I have plenty of cpu power left (as per the cpu meters), why would I be running out of steam for my softsynth?  Certainly, the plugins by themselves weren't causing any problems; my guess is that I could have put in a ton more and still been OK cpu-wise.

In this case size does not matter. The plug-in by design must introduce latency in order to work properly. Plug-ins like the transient shaper are not intended to be used while tracking.

Geoffrey
Well, I had a transient plugin on my kick too, so I will check to see whether that was the main culprit.  I still don't understand my original question:  If I have plenty of cpu power left (as per the cpu meters), why would I be running out of steam for my softsynth?  Certainly, the plugins by themselves weren't causing any problems; my guess is that I could have put in a ton more and still been OK cpu-wise.

Just make sure to save the project after removing it because you have to close the project and open it again for the lag to disappear...