pi = 3.141592
root 2 + root 3 = 3.14626 etc
the answers are the same to 2dp, so any calculation that does not ned to be precise could use it as a substitution, but in pythag the minute decimal places can affect results. (since there are 57.2958 degrees to a radian - which is 4 decimal places NOT 2) it is therefore benificial to have at least a 5 dp accuracy with all calculations (eg at least 1 more dp than the required answer format).
many people will tell you different things. I would not use root 2 plus root 3 due to the fact that many calculators will not compute the input.