It is a difficult question to answer because I don't believe that Maugham ever makes it quite clear what it means idiomatically. Literally it just means something along the lines of "could be much worse." In "The Lotus Eater," Wilson utters the phrase when he compares the twenty five years he will have on the island to the forty that "the mythical German" had after falling in love with Capri.
Idiomatically it appears to go along with some of the bent of the story. Much of the feeling of the story is about the way that things could be worse or this idea of Wilson who decided to take the simple road to happiness and had planned on ending his life when the funds to keep him safely and in the form he desired ran out. The narrator is curious about him and thinks hard about what his life is like, whether he has made the appropriate choice, etc. In some ways this may very well relate back to Maugham's use fo the phrase as it signifies that choice between something pretty good and something that sounds downright horrible.