One serious argument for using a connectionless protocol is mobile. The reason is that mobile networks have a MAC/RLC layer (talking 3G/4G here, e.g. LTE) and t

One serious argument for using a connectionless protocol is mobile. The reason is that mobile networks have a MAC/RLC layer (talking 3G/4G here, e.g. LTE) and those layers have ARQ (in other words retrans). At times, those re-trans can spike (sudden Signal drop for example). That will blow the RTO on TCP and you get needless TCP retrans. This is where you have to competing retrans mechanisms flapping. The obvious fix would be for the mobile operators to terminate the TCP flow at the base station and use the Hybrid ARQ mechanism, although that could happen eventually, but would mean a lot of re-design for them i.e. cost. So if your app is going to be on mobile, it might perform better using a connectionless protocol depending on the situation.