On great many a camera, the lack of an external microphone input is a severe downside. This can go so far as to overall ruin the usability of an otherwise excellent piece of kit for video production. If you do not have an external microphone input and are forced to use built-in mics in your camera, your video will bear ‘amateur video’ all over it. One infamous example of a camera lacking a mic input is the mostly great Sony a5100 mirrorless CSC, a versatile and affordable APS-C sensor camera. Unlike the almost equally affordable Sony a6000 — which at least has some proprietary input for an external mic (more on that below) — the Sony a5100 neither has that nor a hotshoe at htat. A real dealbreaker against the a5100.
The Sony a6000’s external mic ‘fix’ with the proprietary mic connectors behind the hotshoe still is bad enough, actually it should be treated as an overall LACK of external mic inputs altogether. most serious filmmakers do just that!
I am currently in the process of testing those options on the Sony a6000 though and will report on my findings in more detail later.