This is a middle-ground between "servers:" and "defaults:"; where the server can be configured (i.e tls, realname, nicks) but not connected to unless /connect <server> is called.
There are a number of reasons one would want this functionality; but for me, it is to mitigate correlation attacks - where if two accounts auto-connect at the same time, a person could eventually tell they belong to the same person.
I haven't looked at the source yet, but one nice solution is to add a server config called autoconnect: which defaults to true - preserving normal behavior.
A second solution is a separate section (maybe manual: ?) where servers could be configured and matched when /connect requests the same server.