The Kalends, Nones, and Ides: Three Etymologies 

I am pretty ignorant about Rome but time related things can be very, very, veryyyyyyyyyyyyyyyyyyyyyyyyyyyYYyyYYyyYYyyYY significant to people, don't even have to be ancient ones. There are relatively recent books, barely 100-150 years old about Germany that outline many significant dates and times, for all sorts of things, from big stuff like farming and livestock, to little stuff like stepping on a hair at some day and scrying your future spouse from the color of it. As well as nooks and crannies that the 'new' calendar brought with it. Like the last week or so of December is regarded as a special time, an ill/forboding one where things aren't so good. (sadly I forgot the name of that...despite being German myself) Modernity is very loose about these things, but I wouldn't be surprised if this kind of stuff was super important to the ancients.

Its importance was mostly linked to agriculture and religion/religious holy days, so no it wasn't pointless, on the contrary I think what they've created would have been seen as mild back in those days compared to other nations like the Egyptians and the Sumerians.

it was important, ya know

If you think this is pointless, go back in time and try explain the summer/winter time nonsense to a Roman. Or to any person with brain cells walking the Earth today for that matter.