I use it because there is a Check for update option, where you can right click on a downloaded file and if a newer version of the file is available online, it will download it and replace the previous download. I can click on one my download folders in IDM, press Ctrl A to select all of the files and then right click and select Check for update, or press Ctrl S and it will check every file in that folder for updates and download any it finds.Curious to know the reason behind IDA Pro.
I was previously doing this with FlashGet. But the feature was removed in version 3 and the old 2.x releases are fairly buggy.
IDA is not particularly fast at downloading files. But I mostly use it to check for updates, rather than to speed up downloading.
I'm not aware of any other download managers which have a similar feature.