According to Arch wiki: Users of CPUs belonging to the Intel Haswell and Broadwell processor families in particular must install these microcode updates to ensure system stability and security. But all Intel users should install the updates as a matter of course.
I'm not sure about AMD microcodes, but Arch has them included in linux-firmware package and no other action is required according to their wiki.
I get "intel-microcode" package as an install recommendation on many distros from their Driver Manager (Arch has the package as intel-ucode AND it is in .img format, while from Intel website it is in .dat format, I don't know why, I guess it is in .img format after working with it with iucode tool) . After installing, it is automatically applied. Arch needs manual steps to enable it in their kernel.
Well, but I'm sure you know how to implement this (I don't). :D
The update can be then verified by: $ dmesg | grep microcode
Oh, and I hope "Third Party Repository" is correct tag.