In short, a semi-modular synth is the same as a fixed-architecture synth, except it has patch points that enable you to reroute signals for more flexibility. Semi-modular synths are not only amazing creative tools in their own right, but can also be a great and often affordable introductory point into the world of modular synthesis proper. You get you can get some of the desired results of a modular workflow without having to dive in head-first, and even the addition of a one or two carefully selected modules can greatly expand the sonic capabilities of a semi-modular synth.