Not that I'm implying that a mechanical pencil is for non professionals, but almoast every professional I see uses a normal pencil. I actually never use a mechenical pencil but I'll try it out these days cause I can really see the pro's.
Most mangakas I've seen sketch with mechanical pencils. Try drafting mechanical pencil for sketching. The 4mm lead sleeve is perfect for ruling out lines etc. Pilot H-325 is a good choice, but its quite weighty for some.
I really use anything depending on my mood - sometimes I want the beautiful variety of wooden pencils in the entire range from harsh to soft leads. Others, I want to be very focused and astart off right with pens. However, unless I sepcifically want to practice with a certain pen/pencil to get used to it better, I sketch with anything that is around.
Wooden pencils vs. drawing pens vs. ballpoint pens vs. mechanical pencils
Ok break down what I believe and what I use. I do use all of the above.
Wooden pencils can be used because they are good for every line weight possible then the mechanical pencil. Mechanical pencils you probably have to feather your lines to get thicker ones or as in layer on top of your previous line. But Mechanical pencils are also very thin lines, and so thats a nice feature, and its also doesn't have to be sharpened. Certain people like a messy board with pencil shaving all over. Although if you like nice thin lines with a thickness to it, you can sharpen your mechanical pencil even finer (like rubbing it on the side) and then using that really tiny point to get it sharp.
Although for some sketching its ok, but both pencils are just about the same idea as if you want to draw with a pencil. Both will smear if they are not sprayed. So ideally if you were to use pencils that have graphite in them, I wouldn't recommend those in sketchbooks. They smear like crazy, and its also that you can't draw on the other side of the page.
If you want good pencils, it would be probably better to use blue or black pencil, or spray fix you sketchbook. Which at this point, spraying your sketch book sounds a bit silly for a rough drawing.
But for like drawing, sure. It all really depends which medium your using afterwards. If its just pencil, then there isn't any worry. If its charcoal, that isn't a good idea. If its paint, at first it might show through and smear a bit, but then eventiually it won't show as much. If its like gouche, pen and other mediums are better.
Well pen, I love ball point pen, since it can be feathered and stuff. Pens just help you bring up confidence a bit more, because when you make a mistake you will know it. I just feel ball points act like pencils. The slight disadvantage though, is that its just feathering, which you can't get a darkness like out of the pen does. Sometimes it cloggs and smears on the other page but not as bad as a pencil. They also tend to fade alot more. I tend to use these for sketches instead of pencil. It even goes well with gouche and some ink drawings.
For the mistake and you know it pen, its ink pens. They build up confidence and really shows that you have to know mistakes anyway to get through. Cons, none that I can think of, only if you buy a pen that bleeds like crazy,doesn't dry as well, that fades over time, or also doesn't suit water mediums well.
Mostly its just preference, and depends on what medium your using, paper, etc.
FYI, about the sharpening the mechanical pencil by rubbing it by the side, a 0.3 pencil can easily produce thin lines consistently, unfortunately it has a tendency to break when applied too much stress.
A 0.5 Uni-Ball Kuru toga is perfect for this job. This pencil rotates its lead as you write, so you get consistent, thin line as a result.
Yes though, that doesn't mean you can't sharpen it still. There are thin and thick leds and I knew about that. Maybe i wasn't clear on that. And also when you draw, your not suppose to apply too much stress anyway. If you want a dark line, go a darker value, or layer it.
I never knew these existed. Though from experience of buying mechanicals pencils at a store, they are more expensive to buy. There is a store in japan town in my area, that sells alot of stationary supplies, and one is mechanical pencils. All kinds, that can cost upto $15 or $20.