Trying to compile list of brief policy reasons behind FRCP and other rules of civil procedure. So far I have:
avoid prejudice
expedite proceedings
avoid unnecessary cost/delay
convenience
end litigation (preclusion doct)
avoid forum shopping (erie)

Care to add to the list?

Most of those just fall under "efficiency." It's just a question of fairness to various parties versus efficiency most of the time. There's also questions of information symmetry versus the adversary nature of the system (for example, in work-product privilege).

Notice pleading (before Twombly/Iqbal) vs. strict Common Law pleading standards
Case management by judges vs. jury trial
Discovery: equal access to information vs. protecting privacy

trans-substantive nature/point of the rules

Enrich lawyers.

Easy pleading
Easy joinder
Broad discovery

All because we hate trials -- a trial is a failure. Irony is that we spend all our time preparing for a trial, in the hope that the preparation information will enable us to settle/SJ/12b6