Though I admit that default seam allowances to pattern pieces can be very useful when the seams are long and more or less straight, most of the time I prefer to mark the exact seam lines on my fabric. Especially when the seams have short curves, like a neckline, armhole or princess seam. The same is true for darts: I like to know exactly where the lines on the pattern were (or where I drafted them) and don’t want to rely on pins or tacks with basting thread.
My preferred way of marking is with carbon paper. I know I’ve written about it before but it’s a long time ago. Apart from the carbon paper, which is also called wax paper, you need a tracing wheel and a table or flat surface you can put the paper on. I use a cutting mat for it.
The way it’s done is marking the pieces first while the pattern is still attached to the fabric, then you take the paper off, flip the fabric over to the other side and retrace again over the lines you made. I use this for almost all patterns that don’t include seam allowances. On those that have seam allowances I mark the notches and other significant marks on the pattern this way. The above pattern piece is a facing of a dress that I drafted and I haven’t added seam allowances to the pattern.
The paper is years old, taped on the back side and still very useful. It will last a very long time. There are of course exceptions to the use of it: sheer fabric and white are difficult fabrics for this. For white I will use white wax paper. Much less clear to see but I don’t want the risk of the marking showing. If in doubt you should always test it first.
For the darts I mark the end points with a small line too.
I learned to sew with exact seam lines (though by basting them, which is a very time consuming job) and like I said before, it’s what I prefer. The pictures above are from a dress I’m making right now. Hope to show you that soon.