Any circular saw ....which cuts from the top of the work, will obscure the cut, at least partially. The blade guard or the shoe will cover the line, especially on small pieces which will need to be secured against movement. The blade rotation is tending to pull the pieces up off the table at which point they may shift if the saw is not pressed down firmly.
Small pieces have no place beneath a hand held circular saw in my opinion as they won't be accurately cut and may prove dangerous if they shift.
Additionally, if you are cutting to a line, by hand without a guide, you will not get an accurate cut. If you are using a straight edge guide, as for longer cuts, you will have to measure twice, once at each end to make your cut marks. I find this a time consuming process and it may lead to non-parallel edges IF you make even the slightest error in measuring or marking.
There is a new jig, the Kreg Rip Cut, which will make parallel cuts up to 24" wide that will eliminate the double measuring:
Overall, a handheld circular saw is more of a rough carpentry tool than a furniture or cabinet makers tool.
However, there are some builders who will swear by their track saws for cabinets or built-ins on site and that's their choice. If you have to make a dado or a rabbet on site, you'll end up with a router and edge guide because a circular saw doesn't efficiently make those cuts. However, many a stair stringer has been made entirely with a hand held on site for sure, but you won't be building furniture with one.