What effect does using a termination resistor that is larger than the characteristic impedance of the transmission line?
On an open end, a short pulse will be reflected and travel back the line.

On a shorted end, a short pulse will also be reflected, but inverted, too.

A resistor dampens this effect, i.e. the amplitude of the reflected signal will be smaller. And for a certain value, the pulse will not be reflected at all. This is the value used for termination.

Usually, transmitted signals are not short enough to be reflected completely, but every edge would cause a reflected pulse, which causes all kinds of trouble.

See also What and Why's of termination?