In regards to what should be studied, strategy or tactics, I came across an interesting quote by CJS Purdy in his book Guide to Good Chess. “Position play is the art of improving your position in small ways when no sound combination is possible.” The first thing you do of course is as Purdy said, “comb the board for a tactic.” The question is what do you do if there is no combination that is playable? And this will be most of the time. Even so, let’s say you play a game riddled with tactical mistakes. For the sake of argument, let’s say in a 40-move game half the moves should have allowed a combination that lost material or lead to a mate. What were the other 20 moves? One should have been making sound positional moves.
Realistically though, unless you’re an absolute beginner, tactical blunders are likely to have occurred on only a few moves. Say you make 4 or 5. All the other moves had to be of a positional nature. To concentrate on nothing but tactical study does not seem to make sense.
Make a lot of positional errors like creating a N outpost for your opponent to occupy, allowing him open files for his R’s and diagonals for his B’s, weakening your K-side with ill-considered P-moves, or any one of a dozen other positional mistakes and you may end up losing in the ending or…allowing him to build up such a superior position that a tactical solution becomes possible.
By avoiding the study of the positional elements of the game, it seems to me the “tactics only” crowd is avoiding what is actually the thing most of the game consists of…maneuvering your pieces around trying to get them into good positions from where they will have the most potential.