I think many of the NIS scan are supposed to be performed in the background while you are still using the PC. On my computer I find NIS traches the performance of my PC and makes it unusable while a scan is running.
After boot it takes about 2 minutes until it is usable. I use drives meter to monitor disk usage and the disk usage sits at 100% for a few minutes. Obviously a lot of this is Windows and startup programs laoding. I have trimmed the startup programs.
After all these things have loaded the computer is still slow and the disk running at 100%. I watch it in resource monitor and it is svchost which many processes use.
I think NIS attempts to reduce the impact of scanning by monitoring CPU and Memory usage. On my PC that doesn't work well because I have a 6 core AMD CPU and 8GB of RAM. NIS may be using a whole CPU but that is only 15% which looks like low usage. Because there is so much RAM it is always using a low amount. I think they should also monitor disk usage or disk queue length to reduce impact on the hard disk. When the disk is running at 100% the system is not responsive.
When I started up this morning the disk ran at 100% for about 2 minutes (that is just normal). After I had been using it for a few minutes the hard disk started running at 100% again (I am not sure if it was NIS because it was through svchost). A few minutes later it happened again and this was because an update had been downloaded and a quick scan run (there was a notification that the scan had completed).
I am near removing NIS because it trashes the performance so much.