Not the person you asked, but I'll take the ques because I am one of those users who used IDM extensively in the past but don't see the need anymore. I started off with DAP or Download Accelerator Plus, it was IDM before the IDM. Back then downloads were extremely slow as most browsers were inefficient af and weren't designed with this usecase in mind, I am talking about single digit kbps. E.g. a single MP3 file of 3-5 mb would take almost an hour or so to download. I remember I had downloaded the trailer of the Kingkong 2005 movie, it almost took me 2-3 hours or more and then it couldn't be played and I had to download some obscure flash video player.
So yeah, a dedicated downloader was necessary because the downloads in browsers kept breaking and were not resumable. DAP and IDM would download over multiple threads and were faster than inbrowser downloads. They would often also support resuming. These days I rarely download stuff outside of torrent. Torrents are handled by qBittorrent.
Even if I need to download a big file like a Linux ISO, I don't see my downloads breaking and inbrowser downloads are just as fast too. 2-3 gb iso downloads in under 5-10 mins for me over 200 mpbs connection. If I occasionally need to download something as big as 10gb or more, I would use FDM, it's a free alternative to IDM and works well enough for my usecase. It's missing some features but I don't seem them as important.