I use enhanced sitelinks with descriptions across multiple accounts, all pretty successfully. I am auditng an account for a friends and the account in questions doesn't use these, seems daft to me. anyhow i am trying to explain the uplift in CTR they would experience by implementing these, is there an "industry Standard" that anybody is aware of. My accounts all have improved since these have been added but they have performed differently making it tricky to take an avg.
Re: Enhanced Sitelinks
1. they take up more screen real estate - your ad simply looks bigger - actually the reason for that is that it IS bigger - that has to be a good thing.
2. they get you more hooks in the water... a client who is searching for something specific might trigger an ad that whilst relevant is not quite as relevant as the sitelink
3. they're free to add
4. Google now also use sitelinks as one contributing element to compute QS and ad rank - so you are penalising yourself by not adding them...
I'm sure there are many more good reasons, but these should be more than enough to make a case....
There is just one small qualifier to add... ads with sitelinks generally get a better CTR - this is true. but, of course sitelinks only appear when ads are in the top positions and, it0s also true that ads in the top positions tend to get better CTR too.... That said, there is still no real reason not to add them.....