The issue at our club is we've allowed virtually all managers to have a crucial say in transfers. It is fine if you are 100% certain you have the right person at helm, which is almost never, however if things go awry and you are forced to part with your manager it creates a very undesirable situation where the next guy has to either work with players he doesn't want or you need to replace them immediately. Happened with van Gaal, happened with Mourinho, happened with Ole. Each of them left a bunch of players you would want to get rid of as soon as possible, and because they all added up over the years the job got even more difficult with time. At a serious club recruitment duties are at least shared between the manager and club management.