I have a computer with Ryzem 5, Radeon and 8GB memory RAM. I'm thinking of buying 16GB for the empty slot to have 24GB, but some people told me that if I'm not careful with memory balance in my RAM slots, there may be problems, slow performance or loss of usable memory. Is that true or is it a myth? Is it better to buy another 8GB stick or that 16GB stick?
To answer this question, we need to dive a bit into how RAM works in dual channel mode. The two sticks almost always are filled the same way, so if you are using 8GB of RAM, both sticks are holding 4GB, and if you are video editing with 20 chrome tabs open and use 16GB of RAM, both sticks are holding 8GB (probably each half of your footage and 10 chrome tabs). If the sticks are not balanced in capacity, the rest of your RAM will run in singe channel mode, giving you a performance loss of about 30% (single channel performance tested by JaysTwoCents).
The second part of my answer is that if you have 24GB of RAM, the OS will use about 20GB of RAM before it stops loading files in from the disk for future use (video rendering). This means that with a 16GB stick it will get to the "slow zone" faster than with an 8GB stick (slow zone is then your SSD).
Conclusion, get 8GB if you are like me and don't do much fancy stuff. If you do have 20 million chrome tabs, you can think about that 16 GB stick because SSD slow zone is still slower than single channel slow zone.