Unlike manual espresso makers this kind of machine will do some of the work for you - so even an espresso novice can get in the groove quickly and easily.
But, most importantly, this kind of coffee maker also allows you to keep some of the control that comes with manual machines - so you can pick and choose how your coffee will be brewed. You could, of course, buy a fully automatic machine - but here you'll have no control over the final results and that won't suit most serious espresso drinkers.
One big advantage to a semi automatic machine is to be found in the cost. These machines can be way cheaper than many manual makers and can even come in lower than fully automated ones. You can also pick and choose the added features that come with these kinds of coffee makers.
For example, some machines will come with the capacity to make multiple cups of coffee rather than just a single cup at a time, some come with special milk frothers or water dispensers so you can vary your coffee drinking habits by making cappuccinos or americanos if you like and some come with cup warmers.
It's even possible to buy some of these machines that will be compatible with the new pod coffee systems which could make life even easier.
One mistake to avoid here is to make sure that you buy the kind of machine that will suit your coffee needs. All too often coffee lovers buy makers simply because they look good. To get the best value you need to make sure that you buy features and functions that suit your coffee drinking needs.
Also see espresso machines for more details.