Real mechanics read the manual that came with the
machine they need to lube,
Correct.
and they also make sure the lube is rated for the
temperature their gear
will run in. Last time I checked viscosity is temperature dependent, so you
might need something "thicker" in hotter climates and something
"thinner" in
colder ones.
Normally the manuals will recomend lubricants (maybe with different
recomendations for warm or cool climates). If so, and they're available,
you need a seriously good reason not to use them, IMHO.
My Myford lathe came with a lubrication chart (some 30-odd oil points
IIRC) and recomended lubricants. Myford sell the oils in sensible-sized
cans (i.e. enough to last a couple of years), and they're not that
expensive, so of course I use them. I also use them on similar-sized
machinery and tools...
For quite a few purposes around the house where
something is old and stuck
and just needs to get moving again (not worth the time and effort for a
rebuild) WD40 works just fine.
WD40 is ideal for keeping rust of your garden spade, but I wouldn't use
it on precision machinery!
-tony