Termination resistors usage
A microstrip is a variant of a transmission line. Just like a piece of Coaxial cable it a variant of a transmission line.

A transmission line transports a signal (from A to B) without affecting it (except for some attenuation) but only when used properly.

How to use a transmission line properly ?


At the input side use the proper source impedance when applying the signal.
At the output side use the proper termination impedance to ground.


If these conditions are not met, you will get signal reflections.

For example, if you do not place the proper termination at the end of the transmission line, part of the signal reflects back and distorts your signal.
When the proper termination resistor to ground is present, it will appear as if the transmission line "goes on for infinite length" and there will be no reflections.

This also applies to a microstrip line so yes, you need to terminate it properly. Unless you want or you can tolerate to have signal reflections of course !