Well, the best way to learn is probably to admit a CHF pt and go home and read CHF in Harrisons/CMDT, but I don't think you can read those books cover to cover and retain much. I'm not the smartest guy (200 on Step 1), didn't read anything during residency, read/reviewed MedStudy 5x and scored in 80th percentile on boards. On consult rotations where I read the MedStudy section before, I also appeared a lot smarter than I am
Agreed. My opinion is however, also that as a med student, you have to develop a way to approach things (esp in IM). I have fortunately (or unfortunately!) read quite a bit of harrisons - while I agree there is almost no use reading chapters like glomerulonephropathies without a goal in mind, basic chapters like CHF, ARF, stroke really help you to develop a good approach towards medicine.
Even if you read harrisons once - then go to board review books, it helps a lot. I will not state my board score because I do not know if there is a correlation between those scores and having read harrisons or not, but I can say for certainty that those scores (on step 1 and CK) itself opened doors for me, and I can attribute that to the approach (and love) I had developed for IM because I read Harrisons. Its hard to explain, when you read that book, the concepts become a part of you for life.
My sincere advice would be, if you have the time, read harrisons with an objective. E.g. if you are focusing on CNS, then decide the common cases, and read those e.g. stroke, MS, GBS, MG. Obviously, reading it up after seeing a real patient is gold. Then follow it up with a board review book. Those concepts become a part of you, man.
Also I can say for certain that harrisons is not enough. You will probably never master EKGs by reading harrisons. But basic principles, and I believe thats what you were asking for - there is no better book to develop concepts IMHO, and third and fourth years of med school are the right time to build those concepts.