A strong lesson start routine is critical in big secondaries. They set the tone for good behaviour and quality learning, as well as being effective learning in their own right.
They are not too difficult to implement or scale, and become more effective the more routinised. It's a no-brainer for me.
A really thoughtful discussion of Do Nows here, some of the things that can go wrong, & ways (&reasons) to potentially fix them. Most things only work if done well so it's a legit question to ask if it's worth it. My own answer: Yes, Do Nows are worth it, but still valid to ask.