There is a value to Fish ID, and it has a lot to do with how you see, experience, and remember your dive.
Many decades ago, some researchers did some tests and decided that a certain ethnic group (I can't remember which) had some kind of biological problem that prevented them from seeing a certain color. Eventually they realized it was not that they couldn't see that color; it was rather that in their native habitat, that was not a color they encountered, so their language did not have a name for it. Not having a name for it had an effect on their perception and memory that made it seem as if they couldn't see it. The researchers eventually realized the importance of having a name for something. It allows you to pick it out from a group, observe it more clearly, see its details, and remember it. Learn the names for different fishes, and you will be able to pick them out from the mass of fish, see their details, and begin to observe their characteristic behaviors.
Observing dish flitting around a shallow reef is a different experience once you realize that those striped ones moving about erratically are sergeant majors trying to protect a batch of eggs--that purple splotch behind them. That tiny fish jumping at you is a damsel fish protecting the patch of algae it has been carefully cultivating. That bunch of little yellow fish are waiting for a bigger fish to come up to them, open its gills, and have the parasites cleaned off. (If you hang around for a while, you might get to see it.) That trunkfish feeding on the coral is first blasting it with a puff of water from its mouth to clean it off before picking out what it wants to eat. (Get really quiet and you can get close enough to see it, and it looks pretty cool.) That cowfish over there is following that big midnight parrotfish because when that parrot chomps down on a bit of reef, the resulting fragments floating about will have edible tidbits that the cowfish can dart in and nab.
When you are done with a dive like that and someone asks you what you saw, you will have a lot of memories to share.
Or you could say, "There was a bunch of fish."
Many decades ago, some researchers did some tests and decided that a certain ethnic group (I can't remember which) had some kind of biological problem that prevented them from seeing a certain color. Eventually they realized it was not that they couldn't see that color; it was rather that in their native habitat, that was not a color they encountered, so their language did not have a name for it. Not having a name for it had an effect on their perception and memory that made it seem as if they couldn't see it. The researchers eventually realized the importance of having a name for something. It allows you to pick it out from a group, observe it more clearly, see its details, and remember it. Learn the names for different fishes, and you will be able to pick them out from the mass of fish, see their details, and begin to observe their characteristic behaviors.
Observing dish flitting around a shallow reef is a different experience once you realize that those striped ones moving about erratically are sergeant majors trying to protect a batch of eggs--that purple splotch behind them. That tiny fish jumping at you is a damsel fish protecting the patch of algae it has been carefully cultivating. That bunch of little yellow fish are waiting for a bigger fish to come up to them, open its gills, and have the parasites cleaned off. (If you hang around for a while, you might get to see it.) That trunkfish feeding on the coral is first blasting it with a puff of water from its mouth to clean it off before picking out what it wants to eat. (Get really quiet and you can get close enough to see it, and it looks pretty cool.) That cowfish over there is following that big midnight parrotfish because when that parrot chomps down on a bit of reef, the resulting fragments floating about will have edible tidbits that the cowfish can dart in and nab.
When you are done with a dive like that and someone asks you what you saw, you will have a lot of memories to share.
Or you could say, "There was a bunch of fish."