I was thinking about this question and really like John's answer that whatever you don't want is what is the biggest waste of money.
Another way I was thinking about it is: what areas have the biggest propensity to waste money, with wasting money defined as: spending more than what a reasonably efficient operation would spend. For example, if everyone else in a particular market is spending X on golf course maintenance, and you are spending double that for no particular reason, then you are wasting money.
Admittedly, most of the courses that I see are failing in one way or another, so it could definitely be a skewed sample, but my sense is that other clubs have similar problems, they just have the revenue to cover up the issue. If your club is sinking, you would think that someone would say, "let's just spend a normal amount on XXX" instead of what we are. But nearly every club that I see has at least one area that is a disaster, and it may surprise you that it is different in almost every case.
On the daily fee side, as Rob says, it's usually in the clubhouse/F&B. I think COVID has really opened some eyes that a full restaurant is not necessary, though. I don't see a ton of waste in maintenance, as a matter of fact, it's probably just as common to spend too little.
On the private side, it's all over the board.
It will not be surprise that the majority of the clubs I see are not doing a good job in F&B. And my standards are pretty low. Losing money is common, but if you're sinking, you should try to do better than lose $1M a year on F&B.
Golf course maintenance is probably the second biggest culprit. I've seen a LOT of clubs in distress where they are spending 50-75% MORE than everyone else in the market, and it ain't because of the design. That's hundreds of thousands of dollars. It's usually labor, although with excessive equipment leases are pretty common. I saw one club that had been struggling for a number of years, yet their board approved a lease package that cost $400,000 A YEAR, and it wasn't like conditions were bad before that. It included a new $70,000 BACKUP fairway mower and a $25,000 BACKUP aerator among other things that they didn't really need. And yet there were rocks the size of golf balls in the bunkers because that wasn't a priority. The club went bankrupt, by the way, because they were losing about $400,000 a year.
Right behind is G&A and it is a huge rabbit hole. It's mostly overpaid staff or too many staff members. I've seen clubs struggling, yet paying $350,000 for a general manager, or somehow finding enough work for 5 full time accountants. And I've lost track of the number of places you can find $10K here and $20K there in this department. $15K for a postage meter (plus the postage) when everyone is emailed their statements, yep. $25K a year for a copier, sure. The list goes on and on.
Property taxes can be a huge waste if you're not all over it. A buddy of mine does tax appeals and saved courses as much as a hundred thousand a year.
I find very little waste in the Pool, Tennis, Fitness, Pro Shop, or Range.