Well, where do we start? Unless managed in the right way, multiple sites are going to cause your teams a headache.
For your brand identity, it’s tough to keep a consistent brand across multiple platforms. Every time the brand changes, even if it’s just a small change, this will have to be replicated across every site. That’s a lot of admin and development time. That, obviously, is assuming you can actually access the site. Logins could be all over the place, or even managed by a team member who left 5 years ago.
If you’ve used multiple developers and build methods for different sites, you’ll have to keep track of every entity used for each individual website. That means even more admin and lots of hunting around through the CRM. Each update process will be different, and it’ll be hard to plan changes to your sites with any real gauge on timings. Too many cooks, as they say.
From a marketing perspective, your SEO will suffer massively. Multiple websites competing for the same keywords in the same locations will hamper your chances of remaining or attaining the top of the search results. Expect unhappy marketing teams asking for this problem to be solved.