Below is a chart of data of MLB on-base percentage as hitters pass through different counts.  Of course, everyone starts at 0-0, so the MLB OB% average is .324 (note there are some quirks in this data and it is a couple decades old, but conclusions are right).

If the result of pitch 1 is a ball, then the batters on-base % goes to .387.  If the result is strike 1, then the on-base % goes to .256.  That is a HUGE DIFFERENCE and sets up the rest of the rest of the at-bat.  You can see how the results further diverge as the counts play out.

The different between the upper right 1/2 of the box and the lower left 1/2 of the box is the difference between scoring 2 runs a game or 7 runs a game.  Pitchers need to throw strikes early, hitters need to swing at strikes early.  That creates a perfect match-up!