The first reason for most companies to employ a consultant is that they don't have enough time to manage the campaign themselves.
PPC is way too expensive, the competition etc. The crazy testing of ads drove us nuts eg: ad setup, test, tweak, test = failed advert -- ok, start again, set up new ad, test, monitor, re-test.
This was us doing/testing 2 adverts at a time, using the best one and doing the 2nd again, gave nothing but costly fees with little conversions.
Solution, we got a few text ads on targeted sites and suddenly got 35 enquiries in YP giving us business worth = £1750. Sadly, everyone's a pro copywriter when it comes to Adwords it seems, largely without the qualifications to back it up.... and with crazy management fees on top of your PPC fees, its a hiding to nothing for many businesses.
We had a client who was chucking £200 a month on Google PPC for a hospitality campaign, he used us and got 100 targeted visitors to his website, and 10 clients used his services. My view is to go out and source targeted/relevant paid ads, as the visitors will be more likely to buy than a bunch of 'check it out' punters. You don't want window shoppers, as that's what everyone else gets - you want visitors who genuinely want to be on your site, not passers by.... Passing traffic doesn't pay, never pays, or at least significantly reduces that chance of sales.