Should you rent or buy a tuxedo? Well, it all depends on a lot of different factors. How often you wear a tuxedo is very important, because they do not come cheap. If you are going through any significant physical changes, such as losing or gaining 20 lbs. in the next months, it is definitely not a good time to invest in buying a tuxedo.
However, if any of your potential physical changes are stabilized, you don't expect significant changes in your size over the next year, and you wear a tuxedo at least once or twice per year, it is a good consideration to think about buying one.
The advantage of buying a tuxedo is that it will not have been worn a hundred times by others before you, it will fit you properly and it will make you feel really good about yourself, in that you can both afford to buy a tuxedo and you have events to go to that require you to wear one. Classic black tuxedos, worn at black tie events, follow a standard dress code and rarely, if ever, go out of style.
As long as you take good care of your tuxedo, store it properly between uses, it should last you a lifetime unless of course you suddenly gain 20 lbs. There is nothing any tuxedo can do to accommodate such weight gain. That is best left to be dealt with at the gym.
Investing in a tuxedo is a large expense, not a small one. Rentals in the US are $50 up to $100 for a weekend, but buying a very high quality custom-fitted tuxedo may set you back over US$1,000. You don't want to chisel and cheat with your purchase of a tuxedo, because that would defeat the purpose. Instead you want the highest quality material, made to custom specifications, that fits you perfectly. You are going for class not crass.
Therefore, you will pay for it. Ok, the discount shops have them for half that price, but they are no more than a fancy suit. If you are really serious about this, take a trip to Hong Kong. Get a custom-tailored tuxedo made for you there for the price of the discount stores in the USA, have a blast for the 3-5 days you are there and if possible write the whole trip off as a business expense.
They still do really good tailoring work in Hong Kong and the prices for custom tuxedos and for regular suits as well are very affordable. The cost/benefit analysis goes something like this: Compare the costs of renting tuxedos for the events you expect to attend in the next five years against the cost of buying a custom-fitted tux. If, for example, you think you may attend 10 events in the next five years and rentals will charge you a total of about $1,000 it is far better to purchase a custom made tuxedo, because it will be your own, nobody else will ever wear it and it should fit you perfectly.