I stopped MiniSSDPD, will something bad happen?

I would say there's no issue with disabling this service, assuming you have no need for UPnP (Universal Plug and Play). This is a service which allows for devices to "auto discover" one another on your network and advertise services that they can either provide or are looking for to consume.

• http://miniupnp.free.fr/minissdpd.html

excerpt

I first coded MiniSSDPd as a small daemon used by MiniUPnPc (a UPnP control point for IGD devices) to speed up device discoveries. MiniSSDPd keep memory of all UPnP devices that announced themselves on the network through SSDP NOTIFY packets.

More recently, some MiniUPnPd (an implementation of a UPnP IDG) users complained about the non-possibility to run MiniUPnPd and MediaTomb (an implementation of a UPnP Media Server) on the same computer because these two piece of software needed to open UDP port 1900. I then added to MiniSSDPd the ability to handle all SSDP traffic recieved on a computer via the multicast group 239.255.255.250:1900. You may be interested in reading this forum thread about all this.