I have been using IPTV for about 6 months now.
In a nutshell, IPTV gives you Time Shift feature. It will be more expensive to get this feature in DTH mode.
Also, one gets all sports/premium channels in one single package. there are NO different ESPN, neo, star package, ndtv imagine. All channels come under one single package. It is cheaper.
downside is that the electronic programming guide is inferior compared to DTH counterpart.
Also, there is time lag of a couple of seconds when you change channels.
The picture/sound quality is pretty good BUT not as good as DTH.
Broadband speed does not suffer because of IPTV. I have had no problems.
On the whole, IPTV has proved to be cheaper option for me compared to DTH + Internet service.