It would mean that a large class of problems that have solutions that can be verified quickly can be solved quickly. Which cuts both ways.

While that means most protocols used for cryptography would need to be replaced (hashing, digital signatures, etc) it also means other combinatorics algorithms (traveling salesman, protein structure prediction) would become solvable which may been boon for logistics and/or computational science.

(I think this is correct) If P=NP there will still be intractable problems; they would be ones where the solutions can't be verified in polynomial time... along the lines of verifying the solution is correct is as complicated as brute forcing the solution.

Note: it's been a while since my computation theory class. ;) I am reading over https://en.wikipedia.org/wiki/P_versus_NP_problem and relearning the fine house of cards theoreticians have divided this problem into. There is a "consequences of P=NP" towards the bottom that sums it up better than I can.