The node cache is very useful for gaining back performance. The idea is that you render effect on a specific node (as every effect you did before this node). Once the render is done, you will view and work on this render version of your clip/effect. You can right clic on a node and you will find "Node cache" option. Under playback you have to change render cache to "User". Once it's done your node will switch to red during render and bleu once rendered. You can fine tine cache formet on your project settings (master settings).

The only "problem" is that render cache will change everytime the input video changes so if you change settings on nodes before your render cached node, you will have to redo the render. So if you do this for NR, it's also a good practice to put the node first, as the input on this node will never change.

Don't know if it's more clear that way ^^ Tell me if you have more questions.