Subtitles are an underappreciated aspect of all video experiences.
At the 2020 Golden Globes ceremony, Parasite (2019) director Bong Joon-ho said:
Once you over come the one inch tall barrier of subtitles, you will be introduced to so many more amazing films.
That quote resonates with me because I embrace subtitles as an opportunity to watch a wider array of videos that I could not enjoy because of the much taller language barrier. I also almost always opt-in to subtitles on everything I watch.
It can become a point of tension when watching something in a group since some people are turned off by unnecessary subtitles, but it typically enhances the experience for me. In a mostly visual medium, it is easier to comprehend passing dialog if I can glance at it while also examining the details of a scene. While groups of friends are most likely to vote down putting on subtitles, it is often the most necessary in those scenarios where chatter in the room mixes with the TV.
The sound mixing in many old films has the dialog sound less clear and quieter than the music and sound effects. For fantasy, subtitles spell out character names which makes it easier for me to remember. I have little chance of following the lyrics of a musical the first time I watch it unless I can see them.
There are some situations where subtitles can backfire and damange the experience, but this typically in how they are implemented and are fixable problems. The worst are subtitles that are clearly not properly synced. If they display too far behind or ahead of the audible dialog, the mismatch can become a significant distraction. Sometimes the timing is right, but the words are different because it went through a couple rounds of translation and that can be extremely frustrating. Some types of video, such as stand-up comedy, deserve more specialized timing so the subtitles do not spoil the punchline to a joke. The placement of subtitles is also important because bad placement can obscure an otherwise (usually important) readable part of the scene whereas good placement stays out of the way and can provide subtle context.
I have also noticed that when subtitles are provided for translation, those subtitles will often omit transcribing anything spoken in the language of the subtitles. For example, in Season 3 of Occupied/Okkupert which was recently released on Netflix, there is only the original audio which is primarily Norwegian dialog and the only subtitle options are English or Off. However, the characters will occassionally speak in English and no English subtitles are provided for the English dialog!
Of course, the absence of subtitles is usually just an inconvenience to me while for many people it is a requirement for a video to be accessible. I think subtitles are mostly an annoyance for people who do not want them. So perhaps a reasonable standard would be good subtitles on by default and in an ideal world most videos would be designed with them in mind rather than them being what I assume is a production afterthought.
Unfortunately, we are at the point where subtitles are not always available as an option. We can do better! Web accessibility: Essential for some, useful for all.