In general yes, but with enough experience you start to just "know" where the bottlenecks are going to be. For example, if you know your user profile pages are

In general yes, but with enough experience you start to just "know" where the bottlenecks are going to be. For example, if you know your user profile pages are going to be the most used, you focus more pre-optimization effort there rather than on some admin report that will be run monthly. While it's still "pre-optimization" it's a smarter use of time to spend it where it will most likely matter.