Do you mean value add for the client or value add for your career?
A few thoughts from personal experience as ex BCG, now in industry doing similar work as strategy manager in Uber.
From career perspective, I think it was 80% to, dare I say, 90% value add. Yes it was a lot of slide formatting, preparing presentations kind of work. But once I moved on, I realised these skills are incredibly useful. In any commercial setting, you have to know how to influence people, craft an effective storyline that reasonates with stakeholders. Consulting gives you a very good training ground for this under a very demanding environment, and often you will find your skills are differentiated against your peers.
From a client perspective, I had two personal observations.
Firstly, there is an obvious shift towards helping companies implement strategies. It makes a lot of commercial sense for consulting firms as implementations are typically long term and very lucrative. As such, (and this is obviously a broad generalisation) the overall proportion of “rubber stamp, little client value add, decks that goes no where” type of work is going down.
Secondly, it also depends on your performance. Just like any profession, the top performers tend to get the most interesting, rewarding and impactful projects. When I was at BCG,I saw that we were engaged to build entire new businesses for clients. These projects were like long term startup builds and highly coveted. Whether you got on these projects depended highly on your performance.