When your systems don't talk to each other, the most valuable information in the business goes unused. You can't say how much revenue your website produced last year, what it costs to win a new customer, or which products and accounts carry your margin. So marketing decisions get made on instinct, and every budget conversation turns into an argument nobody can settle.
The losses are quieter than a bad campaign, and they add up. Quotes go out and nobody follows up, so business you already did the work to win goes to whoever called back. Customers who used to order every quarter stop, and nobody notices until the year-end numbers come in. Leads from the website land in someone's inbox, or in a spam folder, and never make it into the CRM at all.