Four things I would like to comment on: 1. Score, 2. Handicap Index, 3. Shot Values, and 4. Competence.
Observations and thoughts over a period spanning about 4 years some current some not.
1. Score - Without changing anything in your game, and using statistics, try and find a course with the lowest rating and slope that complements your strengths (verified by actual statistics not just guessing ... if possible). For example, shortish hitter with great lag putting - look for a shorter course with nice large green complexes. Long, a bit wild, and a weak wedge player - look for a longer course but with rating well below par and slope as low as possible. Every person should be looking for different things and sometimes what looks good on paper does not pan out, may take some trial and error.
2. Handicap Index - As above, using statistics try and find a course/tee combination with the highest slope and rating (that plays just inside your competence level) and where the predominate features match your best skills. Also the course should ideally not have a lot of features that would test your weakest skills, for example very heavily bunkered if bunker shots were particularly difficult at your present skill set.
Three seasons ago I played about 70% from the middle tees at Cyprian (73.3/134/6500). For the last two years I have played 90% at Kingston Fairways (68.4/114/5670).
Average score for the last two years I played the Cyprian tees 91, last two years at Kingston tees, 87. A score of 91 at Cyprian produces a differential of 14.9 while a score of 87 at Kingston produces a differential of 18.4. So while the raw score went down by 4 strokes the average differential went up by 3.5 strokes. I score better at Kingston but do I play better or worse golf?
And a ton of other data like anti-handicap/handicap stability, consistency, total scoring spread, and on and on with how they tie into the picture and why. But I think none of it is interesting as it would require lots and lots of presentation and interpretation of data and discussions of if the interpretation is valid, etc. For instance I think using average scores understates the difference in HCI since HCI is based off 10 best/tournament scores (if any) of last 20.
Bottom line I just wanted a real, concrete example of how the numbers can play out but it is only specific to me. Everyone has to work out their particular situation and what they want to accomplish. Also I'm not advocating just playing one course to manipulate some stat I just wanted to illustrate how score and HCI can be in opposition and hopefully provide some food for thought.
3. Shot Value - This is a tough one. I do not care too much about score or HCI either. I do care about shot values meaning how far did the shot I hit deviate from the shot I planned and visualized. The only way I have found to be fairly objective is to divorce myself from the score. Nothing new, has been stated before, but something to be aware of. For example as a ~15 player I hit most shots consistently poorly but actually played/scored overall OK. But at ~13 I really, really started working on ball contact/control and eventually got to where ~30% of my shots were fairly well struck and 65% were still my typically mis-hit wobblers, the other 5% or so are just really poor. But my HCI actually ballooned 5 strokes or so and only started to reverse itself when maybe 50% or better full shots were reasonably solid and less than 50% were "other". It is just a nightmare for planning a shot when there is a 30% chance it will be semi-solid and a 65% or so chance it will be the old weak shot (or worse). Ball contact/control better overall (but more inconsistent), scoring and HCI through the roof! And yet I play with quite a few that judge the shot value solely by how close it lands to the hole, not how it got there. I totally get that, it just is not something I want to embrace. Again two thing working at odds, on the surface better contact/control can only seem like a good thing but if it comes in small increments that introduce inconsistency it can actually be very destructive to scoring in the short term.
4. Competence - My first season I was blissfully ignorant of what could go wrong and the consequences. I actually got some really good advice as a beginner ... I did not know it was good I just followed it as best as I could, again ignorance. I just flailed away at the ball and was as likely to post 131 as 94. Today I will often draw up a shot and intend to hit it that way, which I do only to find out that while my execution was more or less OK, my planning and visualization of the shot were in some way flawed. But my ball striking had to get to a fairly competent level to experience this. Before that, my decision making was like my first season, blissfully ignorant of what could go wrong. Only when my ball striking became somewhat competent was it revealed that my decision making was actually totally unskilled and unsophisticated. Just another example of how some new circumstance (being a bit more competent at ball striking) can jump up and inflate scores in ways I never would have predicted.
And layer upon layer ... or not ... I think this point was already discussed. Some might seek to minimize and manage this complexity in favour of stability and progression, others might embrace it with the long term view of working through it to the next level with the knowledge that some interim setbacks and pain might be involved. Or a bit of a mixture of both approaches at times.
If it matters I have had indexes from sub 9 to 20 plus. But like I said earlier it is just a number and at present the number says I am a bogey golfer, typical bogey golfer ... eh I do not know, for my part if feels typical yea.