Others may disagree, but I see rental points as a great way to supplement the points you own, not necessarily as a pure alternative to ownership. There are a few reasons:
1) To truly rent points, you still need a points account in which to have the rented points transferred. The only way to have an MVC points account is to actually own a small amount of your own points (usually a 1500 point "Base Interest", the minimum ownership needed to get full benefits). Then the person you rent points from can simply transfer the points into your account and you can use them more or less like your own points (with some limitations outlined below). If you don't have a points account of your own, then the only thing you can do is have the points owner make a reservation in their name and add you as their guest. As Fasttr says, there is risk in that approach that many of us find uncomfortable, but others are fine with not controlling your own reservation.
2) Rented points do not count toward MVC ownership tiers, so if the enhanced booking benefits of the higher tiers are important to you (short stays at 13 months, expanded banking windows, etc), you must actually own enough points to qualify.
3) Rented points cannot be banked or borrowed, meaning they can only be used in their native use year. Therefore, you must accurately project your needs for each year and then hope you don't have to cancel a booking. If you cancel a booking with rented points, if you can't find an alternate use by the end of that use year, the points are lost.
4) Because of #3, you cannot take advantage of what, in my opinion, is one of the most powerful aspects of points - always putting yourself in a position of borrowing points rather than banking. Since borrowed points revert back to their original use year expiration date if the reservation is cancelled, always being in a position where you have used all of your current year points and are borrowing from future years for current year trips gives you the most flexibility if your plans change. For example, we have a stay booked for February 2020 at Marriott Maui Ocean Club. Many of the points used for that booking were actually 2021 points borrowed into 2020. So if we had to cancel that booking, we would have until 12/31/2021 to use the freed-up points (and they could even still be banked to 2022, giving us even longer to find a new use until 12/31/2022). If we had used only 2020 points for that booking, the alternative usage window would have ended 12/31/2020, or 12/31/2021 with banking if canceled before the banking deadline. Rented 2020 points would absolutely expire on 12/31/2020.
For all of these reasons, our approach is to own the number of points that we think we can be sure we're going to use every year, and then use rentals only in those years when we need a few more. If we find we are needing to rent points almost every year, then maybe it's time to buy more points.