When I was a practicing engineer early in my professional career, I remember alumni giving me a glimpse of the future of a typical engineer where the engineer would after a number of years move into a management role managing other engineers. Although I didn’t give it much thought at the time, what I didn’t think about was that moving into an engineering management role might make my engineering skills obsolete. Over the years, I did take a path that led me from detailed design engineering to systems engineering to project/product management types roles. Although I stayed on the cutting edge in terms of industry knowledge, along the way I became more interested in business, and I found that my specific engineering trade skills became anemic and obsoleted.
In business, similar things can happen too. For example, many successful sales executives started in an area such as marketing. Maybe down the road they became field sales people and then grew into roles of sales manager, area director, regional VP, or executive VP down the road. With each advancement, they may have become further removed from trench-level sales work. Or they may have helped the organizations become more specialized in productizing the sales process (e.g., for a large company with thousands of existing customers). In these cases, such executives may have set up separate people doing inside sales, other people doing proposals, other people pulling together the technology pieces of a proposal, etc. The executives end up maintaining relationships with customers at the executive level and having the final say in how deals are crafted and how things shape up. In these cases, the executive plays a tremendous role in the larger organization – the situation may be loosely akin to a general in the battlefield. The general becomes far removed from the front line but clearly has tremendous influence and can command respect without having to "do" anymore.
Down the line, management executives (like some military generals) may have more difficulty in moving from large scale environments to entrepreneurial or startup environments. They become accustom to having many resources and telling people what to do. While such executives may have invaluable knowledge and experience about the rise from nothing to sales monster, they may have forgotten what it is like to actually be in the trenches and/or have to do work. Or they may have forgotten what the rise actually entails (which would be a shame if that is the case). I know of many entrepreneurs who lament about venture capitalists or other investors insisting that executive sales VP of brand name Fortune 50 company should become head of sales for seed stage or Series A stage company only to find nine months and millions of dollars more poor that the entrepreneurs were better at selling an early market product with no brand name than the experience sales lifetimer.
This is not to say that managing only is bad. But managing only will create a specialization (which may be rewarded in its own right), and pursuit of that specialization should be a conscious decision. Some managers balance things out by ensuring that they perform a certain amount of work from time to time or visiting the field often. For example, sales managers may not only have regular, internal sales review meetings with field sales people but also travel with field sales people to visit client prospects. Multiple purposes are satisfied with the manager keeping skills fresh, monitoring performance of field sales, and smoking out end-to-end sales and marketing process problems that may be affecting the larger organization.
There are also tradeoffs with just "doing" too. People that get so focused on execution may find that they cannot scale the model. If managers focus on doing as opposed to managing, they may end up micro-managing, failing to utilize others, or failing to develop their managerial skills.
So what’s the answer here? Personally, I think the optimal choices depend somewhat on the nature of the game one is playing. In some industries (e.g., auto manufacturing), the sales and delivery process tends to require specialization to get scale. "Managing only" may be more acceptable. In other industries (e.g., consulting), scale may be harder to achieve and tend to require sales and delivery processes to be closer together. Managing and doing may need to be closer together.
So all said, one needs to recognize that there are different games that can be played. There are also tradeoffs in the types of players that can fill the roles too, much like a guard plays a different role than a center does in basketball. The key is to both match fit with appetite and skill with the game at hand and also to make sure that the process of renewal (e.g., maintenance, training, retraining) is in tune with long-run needs.