Is it necessary to have a good cpu if you have a good gpu? How much does it affects fps performance in games, as I want to upgrade my cpu for higher fps but if it wont increase that much then I don't see the point?
Both are very important in gaming. If you have a very strong GPU (such as the 1070) but a poor-performing CPU such as a dual-core pentium/FX 6300, then you will EASILY be limited by it. It's good to strike a balance between both, and it also depends on what games you'll be playing. Do note that in the extremes, you're going to be bottlenecked more by a GPU than a CPU, but that is only at the HIGHEST possible tier of gaming.
Both are very important in gaming. If you have a very strong GPU (such as the 1070) but a poor-performing CPU such as a dual-core pentium/FX 6300, then you will EASILY be limited by it. It's good to strike a balance between both, and it also depends on what games you'll be playing. Do note that in the extremes, you're going to be bottlenecked more by a GPU than a CPU, but that is only at the HIGHEST possible tier of gaming.