Here, born in Monza and Monza resident for 13 years of my life. In itself, Monza has a few not too important sights in the Duomo, the royal Villa, the city park and the car racing area. As a base for Milan, the problem with Monza is that has no underground metro (MM) link to Milan (Monza simply refused to get that link, not to become a suburb of Milan). MM links you with the very center of Milan, like Duomo; railway from Monza brings you to Centrale and Porta Garibaldi stations, that are still a bit peripheral to Milan centre. You still need a MM leg - in real life, you will discover that the centre of Milan is 45 to 55 minutes away. - Changing from railway to MM in Sesto S. Giovanni could shave a few minutes. - For some business travellers that are bound to some areas of Milan, other than the center, there could be efficient railway links.
I suggest having a look if you manage to find an hotel in Sesto S. Giovanni, near a metro station; you could get to Duomo in only 20 minutes or so. (In this case, the ticket to Sesto Marelli MM stop is cheaper than the ticket to Sesto FS)