On big networks the LIST command can cause large amounts of data to be dumped to the user (as of writing this post: ~820 kB on DALnet, ~1.7 MB on Freenode). In the old days, when 33 kbps dial-up was considered fast, this could cause the user to be disconnected from IRC, probably due to output buffer overflow ("SendQ exceeded") or simply not replying to PINGs in time ("Ping timeout").

FWIW, I have never had such problems even when using 256 kbps DSL, so the warning could be considered obsolete.

I tried putting together a cheat sheet or reference card. After exploring various possibilities I ended up doing the following:

1. Switch from a Swedish keyboard to an English (international) due to the latter being (in my opinion) superior when writing code as well as still being able to type åäö by alt+a/+w/+u+a/+o.
2. Switch from QWERTY to Dvorak because I like how the keys are positioned (no scientific claims here) for programming purposes (had a look at "Programmer Dvorak" but that was too much).
3. Replace vim hjkl movement with dhtn, dD with jJ (mnemonic: "junk"), K with H and the ctrl+w prefix with ctrl+o.
4. Some minor additions (and unbinding advanced features to start out easy)...

TL;DR - stick to using prefixes where available, e.g. ctrl+a in tmux, ctrl+o (Dvorak)/ctrl+s (QWERTY) in vim and irssi. This seems to have the least consequences and be somewhat cross-platform-friendly.