Advertising and law firms is by and large awful.  Yes, there are some excellent examples, but they are few are far between. 

This example from the US highlights the problem.   Using the 'large and agile' chestnut, a well-worn theme, it is no doubt believed with a passion by the partners.  But what does it say about the firm and they way it works.  Not much. 

And there-in lies the problem.  It is incredible difficult to capture a firm with its various practice areas and different buying patterns in one stand-out advert or campaign.   Corporate advertising all to often highlights the sameness of a firm to its competitors.

Far better perhaps to focus on specific practice areas, where messaging can be focused.  And make sure any advertising is well supported by the full arsenal of marketing tools. 

Otherwise it simply becomes a vanity exercise, and an expensive one at that.