While this is mostly related to the content ranking factors, the overall variance of a website’s content and genre may affect rank too.
If your website has had to evolve as your business evolved, then there’s some chance your website may be negatively affected by excessive variance. Specifically, I think this could relate to whether your site has switched genre, with all or most of your old content dumped, and refreshed with a new and different offering.
301 redirects do come into play here, but if you built backlinks on websites that were related to your old offering and your new offering no longer matches, then your backlink profile loses it’s semantic referral value. You can’t simply preserve rank with a 301 redirect any more because it’s just not relevant.
That would start to send confusing signals to search engines. It might just be easier in some instances to start afresh with a new domain.
One type of variance that would add positively to site rank is the continuous addition of relevant content, or the logical expansion of a business into related subject matter or products.