600mm works best when shooting larger subjects if they are far away: wildlife, such as large birds or animals, for instance, present an easier target in the viewfinder than a tiny little insect, for example. Also the minimum focusing distance makes a difference, too. A nice 600mm lens gives you a lot of safe distance between you and a big moose, and yet you can get a great shot nonetheless! Ditto for stepping back a ways from a gorgeous flowering bush while avoiding the bees, and zeroing in on one particular flower.....
That said, indeed one can get some really interesting closeup shots at 600mm, even though standing rather far away from the subject. I haven't done that much yet with my full-frame lens, but I used to do that a fair amount with my RX10 M4 bridge camera and its fixed lens which also reaches to 600mm (35mm equiv on a 1-inch sensor). That is the camera which spoiled me for the 600mm reach, and its days were definitely numbered when I started shooting with the full-frame camera......
My original intention had been to for a while, several months at least, focus more on macro and such with the new gear and still use my RX10 for other stuff, including shooting the geese and ducks from my deck and on walks around the neighborhood and the lake. That idea lasted until the first time I stepped out on the deck with the RX10 to fire off some shots at the Mergansers when I spotted them on the lake one day in December...... Even as I was standing there shooting, I was thinking, "boy, everything would be so much better with my new camera and that nice Sony 200-600mm zoom!" A look at the results in the computer also seemed to emphasize that point. Could I really hold off and wait a few months? Uh...... So, yeah, a few days later, off I went to the camera shop again, coming home with that 200-600mm lens.....
And, yep, the little birdies play with us, don't they?! LOL! Sometimes squirrels do, too -- they stand there and stare at me, and then just as I get the subject nicely focused and framed in a good composition, they turn and dart away! Aaagggh.....!
Since I bought my 200-600mm last January I haven't had much opportunity to take it anywhere away from home, and so most of the shooting I've done with it has been just off my deck, with the lens supported by my hands and also the railing of my deck, although I can and do handhold it. I still need to get a Wimberley gimbal head for the tripod and/or monopod. The lens has internal focusing, it doesn't protrude further out when actually being zoomed, which while advantageous in some ways also means that the lens in its resting state is still always long and large, a bit awkward for an older, slender, petite person like me to handle, but I manage nonetheless! I love that 600mm reach......