Are subtitles (often) necessary? As mentioned in this question, in many Chinese videos, particularly those coming from large media outlets, there are subtitles. I am wondering to what extent experienced Chinese speakers (native or not) find these necessary. By necessary, I mean that you are able to with pretty good confidence "recognize" all the words that are being spoken.

Naturally, it makes sense to add subtitles if the language being spoken is something else entirely. For example, Classical/Literary Chinese (in a historical drama, for instance), a different Chinese variety is being used (or the person speaking has a very strong accent), and so forth. Likewise, in music (where listeners don't have total access to tonal information among other difference), I could understand how subtitles might be necessary in these cases.

But what about in other genres, such as news reports, cooking videos, etc.? 

As a non-native speaker, I find reading subtitles as opposed to actually understanding what is being said as a hindrance to practicing listening comprehension, so I try to listen to things like podcasts or videos without subtitles. Nevertheless, I do spend some time watching (Chinese) subtitled videos and wonder if many of the spoken words in these videos can be understood "on the fly" by Chinese speakers without visual aid.
TL;DR

Subtitles are not necessary.

Large media

Large media and news programs often supply subtitles, because they have more resources. The TV companies in mainland China act like public services, so they have to think about people who are not good at Mandarin, or have trouble with listening.

Cooking programs, talk shows

Some do, some don't. Since these kinds of programs are more free-speaking, they don't have scripts, and it would take some extra work to add subs.

Behavior of native speakers

We like subs, it makes you easy to follow. Especially since we always watch foreign videos with subs, we are used to watching with subs, even when we watch Chinese videos.

Can we understand on the fly?

Yeah, we won't have any trouble with watching videos in Chinese without subs, but that doesn't mean we can recognize 100% of the words, because of accent, background music, rare words, speed, etc. I think that happens among English-speaking people also.