Here is the thing boulderers often spend a great deal of time projecting at or near their limit. This means that they are consistently working high above their base level of skills and fitness, further constant projecting means that climbers are getting a low volume of climbing in during any given session and the quality of that climbing is not very high. With CIR and VIR the climber is working closer to their base level of fitness and movement skills and getting a high volume of high quality practice in each session. This fosters long term improvement, and helps avoid getting stuck at a specific level.
VERY WELL SAID ; I find myself in the gym watching others ,and thinking in my head man I want to get stronger and climb them v7s on the overhanging wall ..But today my partners wher all to busy to go outside so Im at the gym , this big guy was talking about how he did 4-v5 and two v6 and thats about his limit ,now at this point I have done about 10 v0and v1's ,then I moved to some v2's and a few v3's to push my muscle beyond the pump . basicly I was adapting the 4x4 method . at the start of my work out a I picked a v0 I have done before ,,climbed up climb down climbed up clim down clim up clim down climup climdown ,,,,,rest for 5 minutes shakeing out arms ,lol,,, no rest in between,, Also when training at the gym if possible ,I will top rope the hardest route I can for the stamina aspect