I want to make sure I have this set properly. I tried for the first time using Precision. Enable framerate target and setting it to 144 which is my max refresh rate for my monitor. Vsync off in game. Does this sound about right? Would it introduce any kind of lag or effect fps drops? I noticed Precision reporting 135 fps. I did not see it ever go past that. I think its a good thing if I read correctly. Suppose to set it just a bit below actual refresh rate. Was noticing some tearing going above 144 fps. This is my first G-Sync monitor I ever owned. Be nice! 

If 144fps is your desired frame-rate target, then yes. Make sure the checkmark (or the box) is selected, and then hit the apply button. The frame-rate target is a great feature, even if it is implemented in other software.
 
I like using this feat on Batman Arkham Knight, setting at 40fps. 30fps is too low, but 40fps is perfect, and brings a lot more realism to the game.

Ah Arkham Knight. Good example for what I am about to ask. I have the game set to 90 fps in the options. Which is the highest it goes. Now since I set my target to 144 in Precision. Would it cause any weird issues or might I actually lose performance going this route? 

Nothing will happen except Arkham Knight will run at 90fps or lower. If you have the FPS CAP on Precision X set lower than 90fps, though, then the game will run at what you have set Precision X to, despite Arkham Knight set at 90FPS.
 
Precision X will over ride the FPS within game. So, if the game's FPS runs at 120fps, but you have the FPS locked within Precision X at 60 FPS, then the game will run at 60FPS because of the settings on Precision X. It will not make the game run at 144fps if the game has a locked fps setting.

By doing this in Precision. Does it add input lag or make the card run less powerful? Not to its full potential? Kinda like turning on vsync kinda thing? But I use g-sync. 

Non that I have seen. You'll be good, trust me, especially with GSYNC. Precision X is awesome with GSYNC

G-sync will mostly be of benefit if your frame rate stays under your monitors refresh rate, so no need to pin your frame
rates any higher. I found in some cases depending on the frame cap used, things got real choppy and unplayable. To
save myself time and hassle, i just leave V-Sync off and never set frame caps anymore, G-Sync is a marvelous thing ! 
You might want to set V-Sync off globally in NVCP tho, sometimes G-Sync ignores V-Sync settings in-game.

With Gsync, leave vsync off and any frame caps in any software.  let the gsync hardware do its job.

dakon
With Gsync, leave vsync off and any frame caps in any software.  let the gsync hardware do its job.

 
I do. But, I had noticed playing Firewatch. I was exceeding 144+ frames. It started getting nasty with stutter and slight tearing. The second I enabled framerate target in Precision @144 fps. Smooth as butter again. In all games I can control vsync setting wise. I always make sure vsync is set to off and using Nvidia defaults. Its set to use the 3D application controlled setting. 

Fire watch running full screen and not full screen borderless windowed?
 
I love that game and have not had that issue.  It also runs Unity engine, so it should run without any issue.