It's like everything. Either you're a techer, in which case you're almost 100% labs. In that case you make your own tech and sell it too. Or you're not a techer, in which case you never spend turns teching and only buy it.
There's one slight twist here, and that's called the "tech start." The tech start is when you plan to be a commie with all industries, or a casher with all cash buildings, and you lay some tech groundwork for that early in the round. For example, you'd make your first 1900 buildings 100% labs, then research 50,000 points of indy tech, and then you knock down all the labs and build your industries.