Using a standalone debug server application makes it easier to get around the codesigning and debugging restrictions that are built into macOS. Note that this is also the approach used by lldb. Internally lldb uses a dedicated debugserver that implements the core debugger engine - so IDA does the same.
It is possible to use the Local Mac OS X Debugger in ida.app, but you must run IDA as root.
For a deeper dive into macOS debugging, see our tutorial: https://www.hex-rays.com/wp-content/static/tutorials/mac_debugger_primer2/mac_debugger_primer2.html
See also How to launch remote debugging Debugger submenu Start process Remote iOS debugger