For many bowlers, the question often arises: Should you bring a urethane bowling ball to league night and use it? Or will reactive resin get the job done on house shot conditions? The truth lies somewhere in the middle, a grey area, defined only by answering the questions: what is your style, what is the lane surface, and what is the oil pattern?
House shots are designed to help players find the pocket more easily, with a higher lane ratio, meaning more oil in the middle of the lane and less oil on the outside boards. In translation, during a typical league condition, if a bowler misses in, there is enough oil for the ball to hold its line, and if the bowler misses right, there are dry boards for the ball to recover and still reach the pocket. Because of that built-in forgiveness, REACTIVE RESIN BOWLING BALLS tend to perform better for most bowlers and overall for everyone. Reactive resin bowling balls naturally create more angle and backend motion, helping bowlers carry more, thus equating to strikes, even if your release and accuracy are not perfect.
Urethane bowling balls, on the other hand, are known for control and predictability. The characteristics of urethane bowling balls are that they read (hook) the lane earlier and smooth out backend reaction. This characteristic is excellent for shorter or flatter patterns; however, on house shots, those are not great traits for a bowling ball choice. When a ball hooks too soon and loses energy before hitting the pins, especially for players with lower rev rates or higher ball speed, that tends to leave flat corner pins even when hitting the pocket. Moreover, urethane bowling balls accumulate the early oil and spread it further down the lane to the heads, resulting in reactive resins sliding or skidding right before hitting the pocket, and thus the ball deflects.
A rule of thumb to consider... If you are bowling in a league or on open play with a standard house condition, Reactive resin is usually your best first choice because it helps you create angle through the pins and maintain carry. Urethane can be useful for spares or possibly when the lanes get very dry. High-rev players who struggle with resin overreaction MIGHT still benefit from urethane's control, but it will severely hurt their fellow team members.
Ultimately, unless your style suits urethane's smooth, early motion - or you're facing extremely short or inconsistent house patterns - IT IS NOT NECESSARY. But having one in your bag can be a handy option for spares or transition.