The usual rule-of-thumb for break-even in GA aircraft ownership is 100 hours/year.

If a student intends to earn a Comm/CFI within a year, that might be close to 300 hours wich might justify ownership at first glance.

But you can save additional money when renting by only using the the bare-minimum airplane for the phase of training at hand. Ie C-152 for VFR manuevers/XC, IFR C-172 for IFR, and C-172RG for commercial maneuvers.

If you own, you would either need to own an IFR 172RG, or you would end up renting one for at least some of your training anyway.

Also if you don't plan to keep the airplane, the one-time fees and taxes would probably make ownership for one year a losing proposition.

There's definitely some benefit to flying a variety of airplanes in training, but if you intend to own anyway, know exactly what you will need, and that aircraft will also meet your training needs then it might make sense to buy up front.