Just because you used a boat to cross a river, it doesn’t mean you should pick up the boat after you reached land and carry it with you wherever you go. And just like that boat example, sometimes you should consider using teachings or methods the same way.
This piece of advice comes from the Buddhist tradition and asks us (among other things) whether we’re using the right tool for the job. The concern brought out here is reminiscent of Maslow’s Hammer, the idea that if your only tool is a hammer then everything looks like a nail (if your only tool is a boat, everything looks like a river). It also raises some questions about using the appropriate tool for the task and the problem of carrying around a lot of excess baggage. Some things need to be left behind, or they will hinder rather than help.