Generally speaking, when you want to model a part with rounded edges, it is best to use the Fillet command on the Features menu - you can then edit/suppress/delete the fillet feature on the design tree.
Many people do use the Sketch Fillet command though - if you are going to do that, it is best to draw your lines, add your sketch relations, dimension the sketch and then add the fillets last - after your dimensions.
This is why:-
The bottom left hand corner has a dimension to it as you can see...
Because of the tick box "Keep constrained corners"
when this corner is filleted, the system will leave
two crossed over lines - keeping the dimension in place.
This is called a "Virtual sharp."
If we do the sketch fiilets before we do the dimensions, we will not get this.
So, what do we do if we then realise that we needed to dimension to that intersection?
Select one of the straight lines, hold down the "Shift"
key and select the other straight line.
Then, go and click on the "Point"
This will give you the "Virtual sharp" - you can then dimension to that point.
Rory Niles - SOLIDWORKS Instructor.
P.S. The same trick works on 2D drawings as well...