In 1983, I did all my own planning and bookings for a 6-month trip: Canada to Tokyo to Hong Kong to Bangkok to INDIA to Bahrain to France to England, then back to Thailand. No Internet, of course, so I spent a lot of time with the OH&R Guide ("Official Hotel and Resort" Guide). I phoned the hotels myself and booked my own rooms.
I decided that the easiest way to see a lot of India was to book a guided tour for my 14 days there. However, I booked a tour with a private car and driver, and with a private guide. Travel between cities was by air. I got to see a lot of India and in the kind of detail that I wouldn't have been able to alone. It turned out that I was a tour group of only one person -- me. I met other people on the same itinerary with the same tour company -- they travelled together as a group, and on the same flights. The first flight was from Bombay (didn't become Mumbai officially until 1995) to Jaipur. I got to know one couple from the USA very well, and we kept in touch afterwards.
I had only two nights in Bahrain, so I booked a day tour there, which was going to be cancelled since I was the only one to book (a minimum of two was required). So, I told them I would pay for two, and the tour went ahead.
From 1983 to 2011 (when I retired to Thailand), I spent my two-month annual vacations in Asia. During that time, I did the following one-day tours:
Ayutthaya, Thailand
Tokyo, first day there to help get oriented
Seoul, during a mandatory two-night stopover between flights
The above tours were the tour-bus type. I wouldn't want to do more than one day by tour bus.
There was one more guided tour during this period: a four-day tour of Angkor; this time by private car, driver, and guide, again.
Until 2015, those were the only guided tours that I took. In 2015, '17, and '19, my partner and I spent about 2 weeks each time in Japan. We did several one-day guided tours: Nara, Kyoto (three different times), Nikko, Kamakura, Tokyo, but it was just the two of us and the guide -- no group. The guides were local people, experts, certified guides and very knowledgeable. These tours made sure that we got to see what were the most important sites for us; and we were able to get answers to all our questions: a great time! More pricey, but customizable, and far more informative and pleasant than a group tour would have been. In our opinions, good value for money. The rest of the time we were on our own (easy to plan out with the Internet).
In summary, I find that guided tours can have their uses, even though nearly all of my travels have been done without a guide or a tour.