Question about speaker angle

Different speakers = different speaker designs and components = different sonic signatures = different results  = There is no silver bullet answer.

There are three rules to follow.

(1) Hands-on Experimentation 

(2) Read the speaker manual 

(3) Repeat Rule #1.

Tannoy recommends pretty extreme toe-in. I own a pair and I have them toed in as much is possible in their current location. To me, they sound very good this way.

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). 

Pet gave perfect advice

Keep in mind that toe in alters high frequency response, the level of side walls reflection, and the relationship of direct and early reflected sounds.

^^ This! +1

Early side wall reflections are interpreted by the ear as harshness. So you toe in the speakers to reduce the amount of sidewall reflections, allowing the direct radiation to mask the side wall reflections. Sometimes you might even have to have the speakers cross in front of you to do this.