Look if you don't know how to solder and botch the joint you can:
Make the flexwatt run extremely inefficiently
Have connections come apart
damage the flexwatt/wires by overheating them
If the joint isn't insulated properly you can have interference issues (very unlikely but still possible)
Not to mention you can burn yourself pretty badly.
Overall if you don't have any clue how to solder it is much easier to just use the clips. I'm not going to argue this any further.