Well the best advantage would be if your host uses mybilling.info, then you'd be able to use the reseller functions of that.
But if you're just looking to manage clients and accounting (not credit cards, since that would require root access to be able to install whatever you need to install for that... well least cybercash does that I think.... hm.. need to check on that.) You could use paypal though, that'd work.
but you wouldn't be able to setup accounts automatically, that would require root access.