“Do I need a variable speed pump?” is really not the correct question, especially since your current pump is likely working just fine.  Instead you should be asking Does it make sense for me to upgrade to a variable speed pump?  The answer may surprise you!

When considering Variable Speed Pumps (VSP), most people think in terms of energy efficiency and lower utility bills. With good reason, a VS pump can reduce energy usage by up to 90%. Add in available rebates, such as the $300 from the City of Austin and the cost of the VSP can be recouped in as little as one year. The extent of savings and payback is determined by cost of electricity, number of operating hours, pool size, and several other factors. Federal regulation going into effect in 2021 with regards to performance standards in pool specific pumps can currently only be met by variable speed pumps. While manufacturers will improve their single speed pump performance prior to the implementation of these regulations, the focus on variable speed pumps will likely intensify.

Another, and even better reason to consider upgrading may be a cleaner and clearer pool. Variable Speed Pumps offer the following advantages:

Improves Filtration
Regardless of filter type, performance improves when water moves through the filter more slowly, providing more opportunity for better particle removal
Turnover, the time required to filter the equivalent volume of the entire pool, is more effective with lower flow  
Optimizes water features
With more water features, the water supply is split causing too low flow rate for proper operation. With a VSP, the speed/flow can be changed to allow water features to work as designed
Improves UV performance
As flow rate decreases by a factor of 2, performance increases by 100. For example, if a UV system which inactivates 99% of microorganisms at 50 gallons/min is operated at half the flow rate, it would inactivate 100 times that amount, 99.99%
Less noisy
Operating at lower speeds can decrease dB level 30% or more
Longer product life
Lower speed easier on units
Less heat generated, better for components