See also the 3 part video on spurrious emissions:

youtu.be/ERfNlwH-eEc
youtu.be/FcgYikUHtsY
youtu.be/xaehlw7jGrg

And some results of spurrious emision testing: cqqrz.github.io/projects/tra...

If tou were to build your own transmitter then you'd need to include some filtering to avoid harmonic emissions. Without filtering, the transmitter also broadcasts on other frequencies, often on multiples of your intended frequency. There the pass band filter would help, too.

... unless you have a baofeng. 😄 But these filters would be the wrong one.

Good point though. You don't need and want one unless you operate near another transmitter that causes your receiver to overload (i.e. OVF is displayed on the IC-7300).