This is a general questions: In the production chain of file delivery, when do you want to convert a spot into I Frames only?
For Instance if I have to take an SD MPEG file at lets say 4:2:2 and 25mbps and trans-code to 4:2:0 15mbps ; Do I want the higher quality file (25mbps) in I frames or the very last file top be converted from a GOP to I Frames?
Delivery to what?
Sorry but that makes all the difference.
GOP, at a given data rate, is generally more efficient. GOP can be much higher quality that IFrame.
IFrame tends to be better intermediary for some uses because it's easier for systems to process since it isn't reconstructing frames by using B and P frames looking for information.