If you want to accept payments by credit card, you'll get hassle if you don't maintain PCI Compliance. This is basically a shedload of regulations imposed on the whole industry by the credit card companies.
If you ask me, some of what the credit card companies are demanding with PCI is reasonable. But unless you're a post-grad in network science, significant parts of it are about as intelligible as the third Matrix movie.
Then again, no one's asking me and none of us are being given a choice.
Credit card customers will be more relaxed about you than the credit card companies
Integrating with Braintree helps you with PCI Compliance because ...
If you want to accept card details by phone, that opens you up to the PCI and MOTO issue