Ready made jumper wires are popular for making prototypes and even using them permanently in projects. For me, these are some of the things that come from the various far away eBay sellers(or similar stores), as they are very cheap. The same cheap wires can be bought for more money from various local shops, who are reselling them.
However, recently I have bought a set from one of the big component suppliers, because I needed them in a day, not a month. This, of course, came with the penalty of paying about 4 times more for a set.
The difference in feel is huge: the expensive ones are much thinner and more flexible and seem to lack any bad plastic smells. Next, I measured the electrical resistance including the contact with a pin header, and the picture says it all. On the left, the cheap version is around 0.53Ω, while the good one is 0.09Ω, more than 5 times better. Or, to put it from my experience: I expected about 0.1Ω, which makes the cheap ones 5 times worse.
This means you should pay attention whenever powering anything that draws a little more current. Using 2 of the bad wires for a power supply get you over 1Ω or resistance. I have experienced this with various modules, like motor controls or even radios such as the ESP8266 or the NRF24L01 with PA: drawing some 300mA causes about 0.3V drop on the power supply.
But it is not the absolute drop in the power supply that causes problems, it is the internal reset circuit that can cause a reset whenever the power supply suddenly drops by that much. This is why adding a large electrolytic capacitor near the device solves the problem.
What should you do? Depends on the application. The cheap ones are definitely adequate for most things and the price is better. However, the expensive wires will give you a lot less headaches.