If the upper and lower bounds for a problem meet then:

We can say that we understand the runtime cost of the problem
  • We are ready to implement the solution to the problem
  • The universe explodes
  • The problem is \Theta(n)

The universe hasn't exploded yet.

Just because the bounds meet, it does not mean that the cost is \Theta(n).

We might need to implement an algorithm even if we are not certain that it is the best.

When the bounds meet, then we know for certain if an algorithm to solve that problem is best (within a constant factor).