clarify pipeline stages vs experiments

• discussion blocked by/depends on https://github.com/iterative/dvc/issues/7866

Some features often underused/misunderstood/unknown could be helped by better docs/messaging/onboarding clarity.

• Should there be a page clearly describing the difference between stages and experiements?

Nothing in use-cases/experiment-tracking nor user-guide/experiment-management seems to tell existing dvc repro users why they should bother with/what are the use cases of dvc exp.

It doesn’t seem clear to users what’s the difference between stage/repro (i.e. pipelines) and exp (i.e. experiments).

• A feature comparison table would be epic.

[drozzy]

These two clarification points I’ve found in various places (the latter one from @SoyGema) have been very useful for me as a user:

1. Experiments commands exp produce a git ref, that is how it stores its state.
2. “If you use dvc repro, each time you execute it will overwrite everything without going back unless you commit in between each execution.” “dvc exp run allows to run different experiments, for example hyper parameter changes without having to create a commit for each one”

[jorgeorpinel]

Nothing in use-cases/experiment-tracking nor user-guide/experiment-management seems to tell existing dvc repro users why they should bother with/what are the use cases of dvc exp.

We do mention exp run vs. repro specifically in several places like https://dvc.org/doc/user-guide/experiment-management/experiments-overview#basic-workflow, https://dvc.org/doc/user-guide/experiment-management/running-experiments#running-the-pipelines, and https://dvc.org/doc/command-reference/exp/run.