I find that an excellent caddie is invaluable, particularly on a complex golf course.
That being said, as a former caddie I can usually determine their value within the first hole or two and adjust expectations accordingly. It's a two-way street.
I am reminded of an early morning round in San Francisco many years ago when there were only two caddies for our threesome. I took the Portuguese guy who was in the U.S. for a few months to earn some money, and was new to golf and caddying. The other players shared an "experienced" local. Mine was entertainingly chatty in his heavily-accented English, but did an excellent job of keeping up and watching my ball. One could swear that the other caddie was mute and maybe influenced by a severe vitamin deficiency. Not only was he generally many yards behind trying to carry two light bags, but he didn't rake bunkers, fix ball marks, or otherwise provide advice. By the 18th hole, one of his players had had enough and just threw a rake into a fairway bunker, walking away in disgust without raking. His caddie looked at him with a WTF stare in his face; my caddie and I almost died laughing from the other side of the fairway as we could see things build through the round. My caddie was well-compensated and invited me to visit Portugal and stay at this house. The other caddie probably went home unhappy with his pay and with a low opinion of his clients.
On another round further south, I had an excellent caddie who let me know who was boss by the second hole ("Lou, if you keep making me chase your divots, we're not going to get along"). As a pen and pencil type, I like to know my distance on approach shots to the middle of the green and the hole location relative to that number. The course had no yardage markers and Barry simply refused to give me that information. Instead, he would just hand me a club and tell me to hit it as a percentage of a full shot (ditto on putts). I had a good round going into the 14th hole where he again handed me too much club on my approach and told me to hit it around 85%. I came over the top with a lazy turn off the hips through the ball, hit it long left, and had to hit a great up and down in three for a bogie. Next hole he again gives me more club than I want to hit, we argued, he wouldn't relent, and I hit the ball 30-40 yards over the green into no man's land. Another bogie and Barry stopped talking to me. It got worse from there, but he was such a good reader of greens that when I returned a year or so later, I asked for him again. He didn't have a clue who I was.
The best caddie I ever had was further south off the coast, a guy who had gone to one of CA's fine universities for a year before deciding to take some time off. An excellent player with outstanding social skills, 20+ years later, he still hadn't gone back to school, but was facing a dilemma: his fiancee conditioned their future on him re-starting his education and getting a "regular" job. He gave me his card in case our foursome wanted his services while in the area, but he was booked-up throughout our stay. The only downside of that experience was that our round took 4.5 hours as our two lesser players couldn't pull the trigger without consultation, and we missed the cocktail hour at the home of one of Golf's most beloved.
I generally prefer not taking a caddie, but no question that a good one can help in producing a better score. Fortunately, as I've gotten older, my appreciation of a golf course is not dependent on how I play. Even if it was gratis, I'd prefer playing a course at least for the first time relying on my own wits. It is not a big deal to me one way or another, totally dependent on the club's requirements and the preference of my companions.