There are many ways to look at distribution (the P of place in the classical 4Ps of marketing). Many involve trade-offs.
Rory Sutherland points out in this Cannes-based video that in online marketing the vast majority of effort is focussed on distribution and little is invested in the actual content.
In the entertainment industry, the content/distribution trade-off tends to favour content. The ownership of distribution guarantees an audience and thereby extra cashflow surplus to that which you'd garner if you were limited to selling your output via third parties. But ultimately good/popular content will always find distribution.
However, in most businesses, you don't have the freedom to contemplate the trade-off. If your content/product is not so good or, more realistically, if you're in an increasingly commodified industry, then it's clear that the importance of gaining distribution and the difficulty of so doing cannot be overstated. Furthermore, it seems to me that the disintermediation embodied in online encroachments into offline businesses is not quite as paradigm-shifting as some would have us believe.
Generally speaking, there is a physicality to distribution and the scarcity or otherwise of that distribution shifts the marketing dynamic entirely. It's not so much about where you choose to distribute your product/service in order to most conveniently serve your customers and gain market share. In a world of oversupply, it's much more about gaining distribution share.