I kept search off for a long time due to it tanking the quality of the responses from ChatGPT.

I recently added the following to my custom instructions to get the best of both worlds:

# Modes

When the user enters the following strings you should follow the following mode instructions:

1. "xz": Use the web tool as needed when developing your answer.

2. "xx": Exclusively use your own knowledge instead of searching the internet.

By default use mode "xz". The user can switch between modes during a chat session. Stay with the current mode until the user explicitly switches modes.