I'm not sure about about Liquid Courage for many of the investigators in the core set/Dunwich legacy. To be honest, the investigators who struggle with Sanity - e.g. Roland Banks, or "Skids" O'Toole - also tend to have low willpower, so this isn't so useful for them.
Zoey Samaras can make pretty good use of it, particularly if she has something to give Willpower a boost, and her sanity is low enough to need a little help.
However, I've found it fantastic for... Agnes Baker. Yes, she can't actually take this card herself - but another investigator can, and then use liquid courage to heal Agnes' horror. This lets her use her ability to inflict damage when she takes horror even more often, which is awesome, and her 5 makes it unlikely that she'll fail the test to heal the second horror very often.
So if you're hunting Great Old Ones with Agnes at your side, embrace sociable investigating! Come 'ere Agnes, and have wee dram for yer nerves...