The crowd that is saving for a downpayment for a house or similar short-term goal. You essentially need those funds to be risk-free. A flexible CD is another easy option.
The default best option isn't always to invest except for long-term goals like retirement. It depends on what you want to do. (Reddit flowchart agrees with this)
Also, some of us don't believe in retirement. It's a concept more applicable to blue-collar workers (whose decline in physical ability in old age prevents them from continuing) or people who want to kick-back and relax after a certain age, or be financially independent to pursue certain dreams.
But some of us (especially cerebral types) really love our jobs and are reinventing ourselves every decade or so in order to do new things within our professions. My learning rate is actually accelerating with age because knowledge pays compound interest and I've finally built up a large enough knowledge base for this to be happening at an appreciable clip. I'm in my 5th decade, and I'm no longer as quick with computational tasks but my knowledge acquisition and processing abilities are surprisingly much sharper than they were in my 20s.
I can't see myself ever retiring unless my health completely fails (in which case I have buffer funds for that, but I don't call it a "retirement fund"). My parents have been retired for years and in my opinion they are declining faster than if they didn't.
