NkRebuff - Will it affect my performance
From Riftui Wiki
The short answer to this is: In most cases it will not affect your computer performance to a noticeable degree.
Any addon will add some extra load on your computer as more things are being computed. Please keep in mind that the addon api is still regarded as being BETA by Trion. Sometimes a new Rift patch might change something in the API will will lead into addon performing better or worse. The only thing an addon author can do in terms of performance is to try to do good coding. Through it's life cycle nkRebuff had it's ups and downs. Also keep in mind there's a learning curve involved for every addon developer.
While the functionality of an addon grows over time, it's always a tought struggle to add new features without messing the performance of the user's computers. nkRebuff in it's current version has been optimised to use a minimum amount of addon CPU time. This goes as far as that the addon will recognise which modules it needs based on your settings and just load and process what it really needs to do.
You can expect a addon CPU usage of around 0.1 - 0.3% in idle. If you turn off the buff / debuff recognition the addon will use very few addon CPU even in situations where a lot of things are happening around you like for example invasions and raids.
During combat and most especially during invasions you might see a CPU usage of up to 2-3%. This is due to a lot of buffs and their events being fired. Think about an invasion buff where a large number of players is constantly applying buffs and debuffs to the boss. This will result in a large amount of events being fired. Still you can improve your performance even in these situations. See below on how to do this.
How to further improve performance
If you do a lot of invasions I recommend to turn off the buff / debuff recognition once the addon has learned all it needs to know about your abilities. This setting does not limit the ability to identify debuffs on yourself. The addon should know all important things you can cast after initial setup anyway so the only need to still use this setting is to record new buffs of other players. If you experience a high CPU usage of nkRebuff make sure that you turn of the option 'buff / debuff recognition' in the generic setting section.
Another thing you can do is to deactivate the 'player debuff warning'. This doesn't improve performance as much as deactivating the buff / debuff recognition but it will still help a bit. The downside of course is that the addon will no longer tell you about debuffs being applied to yourself.
How to decrease performance
At first this section title might sound funny to you but there's some meaning behind this. By default the addon will only check for changes once every second. This will mean that there's always a slight delay in things showing up and timers will also be slightly off. If you don't care about performance but do care a lot about accuracy then you can decrease the update interval in 0.1 second steps down to a minimum of 0.1 seconds. This will make sure that timers are much more accurate and that you're notified about new things (mostly useable for debuffs) faster.
Just keep in mind that decreasing the update interval will certainly affect your performance as things are done more often. For most people the default setting will work just fine. If you want to play around with this setting I suggest that you test each 0.1 second step individually to see how low you can go with your computer setup.