Your ISP, or Internet Service Provider, can supply you with everything you need to network your home. Should you accept it, though? I'll give you three reasons why you shouldn't.
Long-Term Savings
Purchasing your own equipment may not save you money in the short term, but it will save you money in the long run. ISPs typically charge $10–15 per month to rent their equipment. If you spend $410* on a high-end router and modem setup, you'll break even in about three years.
*Please keep in mind that this price is based on my recommended configuration of an Edgerouter/Unifi AC Wifi Access Point and a DOCSIS 3.1 modem. Of course, if you use less expensive equipment, such as a Mikrotik hap ac2, you will profit almost immediately.
Total savings after 7 years: $430-760 (savings vary depending on what you buy).
Better Equipment: More Security
Your ISP has access to their router, which allows you to make changes to your network through their web portal, which you can access through their website (Cox, for example). You have no control over the updates or the data that is transmitted by your modem/router. If a vulnerability is discovered, it is at the discretion of your ISP whether or not to patch it. At the very least, when using your own equipment, you have complete control over the situation.
More Stability
Stability of ISP-provided technology is a debate. It's almost always one piece of technology doing the work of at least three pieces of technology. Consider driving a car at 100 mph while reading emails and eating a sandwich. Doesn't it seem like a lot? That's what your internet service provider's modem does. It attempts to direct internet traffic, block malicious requests, direct traffic on your network, and handle wifi and wifi security. That's a lot to ask of a single device. When you divide the responsibilities, you tend to get a better product. Not to say that all all-in-one technology is bad, but most ISP-provided technology has a poor track record from a technical standpoint.