Nimbostratus
NimbostratusI had to refresh myself on this. This link may provide some additional helpful info, as the docs on are a bit lean on the details related to this.
Least Connection balances based on an instantaneous value of the connections. So when a new connection comes in, LTM looks at the connections (L4) to each pool member, and just selects the one with the fewest at that time.
Observed looks at the connection over time. Every second it looks at L4 connection to each member. There is some 'secret sauce' algorithm that I do not believe is public, but basically it results in a ratio weight that is based on the connection to each pool member as well as how quickly those connections are being serviced/closed.
So a "least connections" method is less work on the LTM, but if your nodes aren't equal (maybe some have better processing power" it can result in connections going to slower nodes even though they have fewer connections.
The "observed" method puts a bit more work on LTM (as now it must poll and calculate the weights), but in doing so it attempt to ensure connections go to the pool member that can service them quickest.