One is that if you've ever had a spigot fail you'll find that one accident wipes out any convenience you ever gained. Two is that there is no way of knowing that the thing stayed sanitized during the long wait for the beer to finish. The tiniest leak, even just one drop, creates a petri dish that your beer has to flow over on its way to the keg or bottling bucket. I don't like them, so I don't use them.
Same here. I had a run of 4 batches many years back when I was using a bottleing bucket where all the beers just went south quick. (competition wise I went from 38/42 to 28 scores...) I finally traced it back to the spout of the bottleing bucket where beer had accumulated over time between in the pressed fit clear plastic/red plastic valve. When I finally thought to try and take it appart, I found mold and gunk in it... From that experience, I bought 4 new valves and considered them single use. Later that year (scarred for life ) I switched to kegging.
I for one am very anti valve... unless you can take them appart and clean them!