Swings and roundabouts. If your AVR upscales and de-interlaces in a manner better than your TV/Monitor, then obviously it offers an improvement.
Similarly, if you still have composite or S-video sources that you want to route via your AVR then decoding (from composite/S-video to digital component) makes life a lot easier, as you then can route the analogue sources via a single HDMI feed to your display. This doesn't require upscaling though - as most modern HDMI displays will accept 480i/576i sources (though early displays didn't as the 480i/576i over HDMI spec was a later addition - some displays started with 480p/576p - and required external de-interlacing at least)
I don't have any analogue sources to watch these days - and don't use any of the upscaling facilities in my Onkyo amp as a result. Just straight HDMI video pass-through.