I've got a 60MP camera (Sony a7R4), and I could see the point of a 100MP: extreme crops while still having acceptable image quality in the result. Doing bird photography after a certain point the size and weight of the lens becomes an effectively insurmountable issue (somewhere around the 600-800mm range, depending on maximum aperture) and the only way to get more "reach" is to be able to crop the resulting photo. So I'd never use the full 100MP, but I might discard 75% of it to get a nice print-quality bird image of reasonable size.
Of course you also need a really good, sharp lens to take advantage of such a high-res sensor. Any flaws in the lens or your technique or settings will show up more dramatically in a deep crop. So it's not going to save you money on a shorter focal length lens, it's just going to save weight.
Of course you also need a really good, sharp lens to take advantage of such a high-res sensor. Any flaws in the lens or your technique or settings will show up more dramatically in a deep crop. So it's not going to save you money on a shorter focal length lens, it's just going to save weight.