About RLSA Bid Stratergy
Remarketing lists for search ads (RLSA) is a feature that lets you customize your search ads campaign for people who have previously visited your site, and tailor your bids and ads to these visitors when they're searching on Google and search partner sites.
1. Target & Bid Only - If you are using Target & Bid - You can reach only remarketing audience when they are actively searching for your products or services, so the Adgroup bid is the only bid you need.
2. Bid Only - If you are using Bid only - Your ads will show to any user searching for the targeted Keyword and you can bid more acording to the audience who is actively searching for those terms.
Kindly check about RLSA Strategies
Hope this will help.