Associate
Dont bend your arms 90 degrees as such, otherwise it will turn into a DB press but there has to be a slight bend in the arm.
As far as the advantage of inclining the DB press opposed to doing them flat, you are targeting the upper chest which essentially is the hardest part to build. The lower part of your chest gets worked far more anyway when benching and doing other exercises, and is easier to gain muscle on your lower chest.
On a chest day I personally taget my upper chest first with DB/BB inclines, I have now started using dips as the first exercise to target my lower chest.... but thats just me!!!
As far as the advantage of inclining the DB press opposed to doing them flat, you are targeting the upper chest which essentially is the hardest part to build. The lower part of your chest gets worked far more anyway when benching and doing other exercises, and is easier to gain muscle on your lower chest.
On a chest day I personally taget my upper chest first with DB/BB inclines, I have now started using dips as the first exercise to target my lower chest.... but thats just me!!!