Can number of joints matter

[Charkel]

While working with cables that has the be joined together I often wanna add some extra wiring just to make it a bit longer or just to easier make changes to it later by just cutting of a bit of the extra wire.

But that would add 1 or 2 extra solder-joint cables. Would that have any risk of disturbing the signal if it's not just the current going through?

Of course everything is current but let's say the data wires of the USB cable as an example

EDIT:
Just wanna add that my solder joints on cables are not perfected and often working with thin cables like 7-10 stranded I have a hard time wrapping them together so it's often a strange joint

[RobertHolcombe]

Outside of RF applications its probably not going to present any issues.

From a mechanical perspective, every joint is going to be a potential point of failure. Its good practice from a reliability standpoint to have single continuous runs of wire wherever they are required, with a single termination at each end (whether it soldered, or a connector). Outside of mission-critical applications this isn't really an issue provided your soldering technique is sound and you can be confident in the reliability of the joints you're creating. Anywhere you're joining wires together with solder will become a rigid joint in otherwise flexible wire, so planning to accommodate adequate strain relief for the joint can go a long way in avoiding issues with joint failure.

[rstofer]

At higher frequencies, the discontinuity will cause reflections.  Just something to watch out for.

The entire business of using a time domain reflectometer is based on locating these discontinuities:

https://en.wikipedia.org/wiki/Signal_reflection

[Doctorandus_P]

Signal speed over USB cables varies ... extremely widely.
From 1.5Mbps (any cable will do) to somewhere int the Gbps ( Every small thing becomes critical).

Also:
For reliable connections, you do not want cables to be able to bend at the end of a solder joint.
They break very easily there over time.
A trick often used is to feed them through a hole in the PCB and then solder it a cm or so further on.
(Or add real pull / bend / stress relief).