Are ignored pages a deterrent to good SEO?

Are ignored pages a deterrent to good SEO?

The website I am working on is huge in size and has a considerable number of pages which are ignored. Although, these pages have certain links which are still functioning and bring in a small amount of traffic. However, the website owner has not updated these pages in a very long time and is on a total upgrade. In such a case, do I need to keep these pages or delete them? Would such pages affect the functioning of a good SEO? I am afraid to lose the links and reduce the traffic flow to the site. Please help me out by giving the right suggestion.

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Digital Marketing Agency|SEO UK