Hrqls: are there also positions in which its better to move only 1 piece into you home because it covers an empty spot (and leaving 1 outside your home)

Most definitely. It's more about the distribution than simply leaping over the bar. As nabla says, the 6-5-4 points are the most important. If you're stacked on 6 and 5 or 4 are empty then a roll that stacks the 6 higher is no good to you. You'll only waste rolls later unstacking it (unless you get 6-6). As you'll have no control over those later rolls but right now you have a known roll, why not place the checkers usefully.

Here's an example that I've just made up:
http://www.gellie.plus.com/DG_Extras/MakeBoard/ShowBoard.htm?MatchId=cIkmAAAAAAAA&PosnId=3HauAADc/CUBAA


With the 5-1 you could add two more men to the 6-point. Of the 20 moves shown in GnuBg, the 11/6 7/6 stacker is 17th and a Bad move (-0.48). It's much better to do 7/2 6/5. Putting one on a low point is greatly preferable to stacking. But the best move (it just edges it out) is 9/4 6/5. This builds on the 4-point, which is important because it's very weak in relation to the 6-point, and unstacks the 6-point a bit.

One additional point about the 4-point compared to the 3-point. If you roll a 3 and there's a hole on the 3-point then 6/3 will fill it. The next 3 will thus take a man off. If you have a hole on the 4-point and roll a 4 then you have to move a man deep from 6 or 5 and there's still a hole on the 4-point. The next 4 would thus waste another half a roll. The same applies to the 5-point but it's somewhat less troublesome. When the 6-point is cleared then a hole on the 5-point disappears automatically but a hole on the 4-point will still need the 5-point to be cleared before it disappears.