cmd: simplify exaplnations about plots files being or not in dvc.yaml

per #1881 (review)

content/docs/command-reference/plots/diff.md

@@ -19,9 +19,9 @@ positional arguments:
 
 ## Description
 
-This command is a way to visualize the "difference" between metrics among
-experiments in the <abbr>repository</abbr> history, by plotting multiple
-versions of the metrics. All plots defined in `dvc.yaml` are used by default.
+This command is a way to visualize the "difference" between
+[certain metrics](/doc/command-reference/plots#supported-file-formats) among
+versions of the <abbr>repository</abbr>, by overlaying them in a single plot.
 
 > Note that unlike `dvc metrics diff`, this command does not calculate numeric
 > differences between metrics file values.
@@ -34,8 +34,9 @@ revision results in comparing the workspace and that version.
 💡 Note that any number of `revisions` can be provided, and the resulting plot
 shows all of them in a single image.
 
-Specific plots files can be specified with the `--targets` option. Note that
-these don't have to be defined as `plots` in `dvc.yaml`.
+All plots defined in `dvc.yaml` are used by default, but specific plots files
+can be specified with the `--targets` option (note that targets don't
+necessarily have to be defined in `dvc.yaml`).
 
 The plot style can be customized with
 [plot templates](/doc/command-reference/plots#plot-templates), using the

content/docs/command-reference/plots/index.md

@@ -29,15 +29,13 @@ learning training or data processing:
 
 ## Description
 
-DVC provides a set of commands to visualize metrics of machine learning
-experiments. Usual plot examples are AUC curves, loss functions, confusion
-matrices, among others.
+DVC provides a set of commands to visualize certain metrics of machine learning
+experiments as plots. Usual plot examples are AUC curves, loss functions,
+confusion matrices, among others.
 
 This type of metrics files are created by users, or generated by user data
-processing code, and can be defined in `dvc.yaml` stages (using the `--plots`
-and `--plots-no-cache` options if using `dvc run`). `dvc plots show` and
-`dvc plots diff` can work with any valid plots files in the system, whether
-tracked by Git or DVC, or not.
+processing code, and can be defined in `dvc.yaml` (`plots` field) for tracking
+(optional).
 
 DVC generates plots as HTML files that can be open with a web browser. These
 HTML files use [Vega-Lite](https://vega.github.io/vega-lite/). Vega is a

content/docs/command-reference/plots/show.md

@@ -18,12 +18,13 @@ positional arguments:
 
 ## Description
 
-This command provides a quick way to visualize metrics such as loss functions,
-AUC curves, confusion matrices, etc. All plots defined in `dvc.yaml` are used by
-default.
+This command provides a quick way to visualize
+[certain metrics](/doc/command-reference/plots#supported-file-formats) such as
+loss functions, AUC curves, confusion matrices, etc.
 
-Optionally, specific metric file `targets` to show are accepted. Note that these
-don't have to be defined as `plots` in `dvc.yaml`.
+All plots defined in `dvc.yaml` are used by default, but specific plots files
+can be specified as `targets` (note that targets don't necessarily have to be
+defined in `dvc.yaml`).
 
 The plot style can be customized with
 [plot templates](/doc/command-reference/plots#plot-templates), using the