Hi i am very new to UV mapping ... got couple of newbie questions

I would like to ask ,can planar mapping be the solution to all types of mapping?

like for example a human body ... i planar map from the front view and planar map again for the back.

What advantages do i have if i use shperical , cylindrical or other types of mapping...

my next question is : for example i map a dinosaur, i would map the body and limbs seperately, how do i ensure the mapping is seamless pls refer to the pic

Do i have to sew and merge the UVs?

pls advise

Thank you in advance