There is no point in arguing which mainboard form-factor is better as you can just choose whatever suits you best. Notwithstanding a rather large number of standardized formats, ATX and microATX are the most familiar ones for the majority of users. ATX enjoys a wide following because the large dimensions (305 x 244 millimeters) make it possible to place each individual component in its proper place and endow the mainboard with extra functionality by means of onboard controllers. Full-size ATX mainboards also allow installing more expansion cards but this advantage has lost its importance nowadays. It is only if you want to assemble a multi-GPU configuration that you will definitely need an ATX mainboard. In most other cases a compact microATX one (244 x 244 millimeters) will do just fine. Modern microATX mainboards have also shattered one more stereotype. They are not limited in capabilities and functions anymore. I know of microATX mainboards that are just as good as (or even superior to) full-size ones in terms of specifications, overclockability and fine-tuning options. This explains why compact mainboards have become quite popular.
On the other hand, many users still stick to the ATX form-factor even if they do not intend to install add-on cards or overclock the system. Functionality being the same, it is just easier to deal with a full-size mainboard. It is simpler to replace memory modules or graphics card without taking the entire system apart. There are fewer limitations concerning large CPU coolers. The PCB design is generally more user-friendly, too.
Given the above, it may seem that miniature mainboards of the mini-ITX form-factor (170 x 170 millimeters) have no chance at all, but that’s only the first impression. The much smaller size leads to dramatic qualitative changes when we switch to this form-factor. A tiny mainboard with an integrated energy-efficient processor allows doing without active cooling and a small noiseless system case with it can be easily hidden behind your monitor or among the other electronic devices near your TV-set. Such a computer would be enough for watching movies, listening to music, processing documents and browsing the Web. It can be occasionally used as a second, auxiliary computer but won’t have enough performance to work as a main one.
This is how things stand in general but there are always exceptions to established rules. Zotac H55-ITX WiFi mainboard I am going to discuss today is based on Intel H55 Express chipset and supports modern top-performance LGA1156 processors. Its mini-ITX form-factor allows assembling a fast computer in a compact system case. Despite its small size, the mainboard is equipped with a number of extra controllers and can even overclock the CPU and memory if necessary.