"confer" ("cf.") vs "see also"

comment reposted as an answer, extracted and edited for brevity from https://en.wikipedia.org/wiki/Citation_signal :

Signals that indicate support:

[no signal] - a simple citation of another source.

'e.g' (exempli gratia) = 'for example'.

'accord' is used to introduce other supporting sources to follow up previous citations.

'see' indicates that the cited authority clearly supports, but does not directly state, the proposition.

'see also' indicates additional material that supports the proposition, less directly than 'see' or 'accord'.

'cf.' (Latin 'confer') = 'compare': points to a different proposition, but one sufficiently analogous to lend support.

There are other signals which suggest that cited sources contain background material, or contradiction.