Depends on the route you go but the pros of outsourcing could mean you get more ideas up front.
For example if you go down the route of a site like 99designs which lets multiple designers compete for your work and you choose the idea / design you like best.
You could also engage a few different designers either from personal recommendations or a site like Elance.
The cons might be the cost (if your in-house designer is already on the payroll there's no 'extra' cost like with outsourcing) and also the ability to physically sit next to your designer and discuss play with ideas though with Skype, Dropbox and similar tools you should be able to offset some of that.
Hope that's helpful, but let me know if that's not what you had in mind when asking.
(PS I talk about 99designs / Elance in an article / video I did previously here: http://nickdavis.co/web-design-outsource-templates/ )