Let me summarize from my own experience. Starting about 1987 I made a serious effort to memorize chess information. Over the course of 30 years my chess knowledge has become somewhat extensive, having memorized several hundred pieces of chess information. In addition, I have memorized hundreds of technical things related to my job and about a hundred phone numbers.
Ideal learning is one where we don't memorize but learn by doing it. In this case we are developing a skill and not just cramming facts into our brains. This is how I approached my computer classes 30 years ago, where I would spend most of my time in the computer labs doing my assignments and as a result I never had to study for tests because I already knew the material.
There are disadvantages, however, to the approach of "learn by doing it":
1. The amount of time spent is rather large. If you need to know specific facts quickly, then memorizing is more efficient. A simple case of this would be learning a phone number. If you dial it enough times you will eventually remember it, but you can learn it faster through wrote memorization.
2. Not all facts can be learned from experience. In the case of the type of work that I do, some book learning is required. The same thing can be said about chess.
3. If you don't use the information, and make no effort to review it otherwise, no matter how well you know it now, you will eventually forget it.
My experience tells me that there is no such thing as short term or long term or permanent memory. There are only degrees of how well it is programmed into our brain. The more we are exposed to something, the longer it takes us to forget it. Over time we can know something well enough that we only have to review it once a year or even longer to retain it.
Our brains, however, are inherently forgetful. To make matters worse, as we learn new stuff, our brains have a tendency to forget other things. Learning fact "A" will push out fact "B." Only by learning fact "A" and still review fact "B" can we retain both. (It helps if fact A and B are related, because studying them together is easier than studying them separately. For example: the phone numbers 268-2584 and 825-2689 have enough common digits that it was easier for me to learn and review them together. If I tried to learn them separately then I would be more likely to get them mixed up.)
The technique that I developed 20 years ago allowed me to memorize over 2500 different things. This technique involves keeping a list of things that I memorized, organize everything on that list by categories relating to how well I know them, and have specific dates for reviewing individual items. Some items get reviewed once a day because I don't know them very well, but other items that I know better get reviewed less often. When I review an item, and remember it, I move it to the next higher category and set a date for when I will next review it.
Actually the list is a more complicated version of flash cards. The list consists of questions and answers. If I get a question right, then I move that item to a category that gets reviewed less often. This list might look something like the following .....
Once very day: (03-18) http://www.entertainmentjourney.com/g0001.htm
Once every 2 days: (03-19) http://www.entertainmentjourney.com/g0002.htm
Once every 3 days: (03-20) http://www.entertainmentjourney.com/g0003.htm
Once every 4 days: (03-21) http://www.entertainmentjourney.com/g0004.htm
Once every 5 days: (03-22) http://www.entertainmentjourney.com/g0005.htm
Once every 7 days:
Once every 9 days:
Once every 12 days:
Once every 16 days:
Once every 3 weeks
The numbers in parenthesis represent dates on which I plan to review specific items. I am constantly promoting and demoting items between categories depending upon how well I do on each item.
Each of my categories represents a time frame of how long I wait before I review an item again. These categories range from once a day to once a year, and I generally try to increase the time frame by 1/3 from one category to the next. I tried using different factors larger than 1/3 and they didn't work as well.
I was told recently that some chess professionals also keep lists of things that they have learned.
The disadvantage to my wrote memorization approach (as opposed the learning by doing approach) is that if you cram as much raw information into your brain as I have then it takes a serious time commitment to retain that information. At present I spend about 45 minutes 4 times a week reviewing what I have learned. Three hours per week might not sound like a great deal, but for most adults free time is precious and in limited supply.
If I add no new information to my memorization list then the amount of time it takes to review actually goes down because I promote items to categories where they get reviewed less often.
One way to avoid spending too much time on the list is to only add 1 to 2 new items per week.