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!