Connect and NetCon cannot be used for the same purpose.
Connect sets up an electrical connection between two neighbouring cell compartments thus introducing continuity of the intracellular fluid into the model. This electrical continuity is for some mechanisms extended with a chemical continuity by introducing diffusion between the compartments. This connection betwen two compartments is always there and introduces extra differential equations.
In the context of conductance based models NetCon is mainly used for dealing with synaptic communications. In the event system underlying Netcon action potentials firing times that occur in presynaptic cells (source) are communicated to the synaptic mechanism on the postsynaptic cell where they can be used to switch on a synaptic current. The relation created only occurs around action potential generation after which the two cells with their synapses are decoupled froom each other and follow their own set of differential equations until the next event occurs.