Question about speaker angle

Generally speaking, the more you toe-in speakers, the more solid and precise the center image will seem, but, this comes at the expense of a less expansive (wide) soundstage.  You need to experiment, that is the only way to know what is right for your situation and personal taste.  the same actually goes with all aspects of speaker and listening position placement--a lot of trial and error is required.  Don't for get to also dial in speaker height and rake angle (how much the speaker is tipped backwards (i.e., the degree to which it is angled toward the ceiling). 

Not only is the dispersion pattern important, but also the distance one sits to the speaker-another thing that the designer starts with a particular assumption that might not fit one's particular setup.  High frequency energy dissipates faster than do the lower frequencies, so that if one sits farther back, the highs sound attenuated compared to close in listening.  At an audio show, I once heard a speaker built around a very expensive Voxativ driver that sounded extremely bright when I sat in what appears to be the sweet spot; but, when I went back another fifteen feet (in theory the angle actually put me more directly in line, so highs should increase), the sound became much better balanced.

The high frequency balance can be adjusted somewhat by changing the toe-in to compensate for such effects as distance from speaker, room reflections, etc.  But, to me, the biggest change one can expect is on the focus of the center image (toe-in increases focus) and the left to right spread of the image (toe-in decreases the spread), such that one is trying to find the right compromise.