Thanks mad_jock,
heplfull your answer is. I understand that knowing pitch value is of a help only if used with other readings such as rate of climb/descent, speed etc.
If for instance , during a dark night, one has at his disposal only pitch and speed values, he cannot precisely insure that he is climbing, descending or in a level flight. A 5 degrees pitch reading can mean for instance eather a "2 degrees climb path at an AOA of 3 degrees" or a " 2 degrees descent path at an AOA of 7 degrees".