It allows you to diversify. You don't have to have your money held hostage by one entity. Coinbase is known to give people shit and they are overwhelmed right now. Bitpay allows you to load up to 25k, have a $3,000 ATM limit, and $10k spend limit per day. Coinbase limits were shit last time I checked. Something like 15k for a week and if you want it raised they want to ask all types of invasive shit as if they don't have all your info on record already.
Coinbase can confiscate or hold shit because of their 'source of funds' bullshit. How do these crooks take your money to buy and then when it maybe goes up 10x, they want source of funds? Bitpay has all the info and can just hand it over to the IRS. Retards over at coinbase act like they can't do the same. It's almost like coinbase acting like they don't have the money to give people so they hold folks' shit over bullshit reasons.
Coinbase is how people can get into the game buying BTC, ETH, and LTC. Some people just prefer to have different ways to pull money out instead of coinbase because of known issues with them. Bitpay allows you to pull money out simply by loading your Bitpay card. You even get a routing number that can be used for transfers. Bitpay will be adding support for other altcoins in 2018.
See my response above for more info.