The impact that memory has on the performance of a computer has not been too exceptionally big for a while now. The new DDR generations have been keeping up just fine with the increased speeds of processors and other components and therefore the memory is no bottleneck in most usage cases. Despite the fact that the majority of users did not need more than the speeds of DDR3, it was replaced by DDR4 a couple of years ago. The main advantage of DDR4 is that higher clock frequencies are possible at lower voltages. DDR4 mainly had advantages for servers, since low power consumption is key for servers, however end users also benefited in the form of lower power consumption of laptops.
In general there aren't too many programs that rely heavily on the speed of the memory. Only programs such as the x264 encoder, WinRAR and benchmarks such as SuperPi benefit from faster memory. For this reason we handle the rule of more memory over faster memory.
As we mentioned before we've had test results recently that make us question the aforementioned rule, since some benchmarks showed that faster memory does in fact have a positive influence on the frame rate in games.
Furthermore we've also seen that the type of memory can affect the speed of the IGP significantly. A large amount of people still use the integrated GPU of their processor to game: out of all Steam users 17.4% gamed with an Intel IGP, according to the Steam Hardware Survey of January 2017. Reason enough to research the effect of memory bandwidth extensively.
Dual and quad channel
There are hardly any systems out there on the desktop market that feature a platform that does not support dual channel memory. However there are still a lot of system builders that do not utilize this feature, because they only place a single memory module. The advantage to this is that there will at least be one empty slot available for future upgrades (many OEM systems do not feature four memory slots), however you could potentially have poorer performance as a result.
The situation with laptops is even worse: OEMs tend to equip cheaper laptops with only a single memory module, due to cost savings, since they are apparently available for a lower price. Furthermore the memory module is generally not upgradable. For this reason it's good to know whether you should make your purchase decision based on this specification.
It will also be interesting for people who build their own systems because, as we mentioned before, you can find out whether you should fill up two or four memory slots immediately, or start out with a higher capacity, so that you can upgrade later down the road. You shouldn't leave out the first option because of costs: most memory modules these days are sold in kits of two pieces and these are not significantly more expensive than single modules with the same capacity.
The story does change for the X99 high-end desktop platform. This high-end platform also supports quad channel memory. If you are going to purchase a X99 system anyway, there is no reason to not utilize this feature. However, it's once again interesting to find out whether starting out with less filled slots is better - so that you can upgrade later, or so you can save costs. Also, there is at least one X99 board on the market with only two memory slots, the ASRock X99E-ITX/AC. For this reason it's once again interesting to find out what multi-channel memory can do, and whether quad channel itself is a reason to consider X99.