It's my opinion, but a traditional 'stackable' switch has a very high speed, high bandwidth, redundant bus for the interconnect.   I.e. 3750x.  Which allows multiple switches to be stacked.   On the 2960TS, you are effectively limited to two.  More than that and you lose redundancy and the link becomes ineffective.  Since the 2x 10GbE interconnects would be split between three switches.  A true stack doesn't suffer that issue.  There's no hoping between switches to get to another stack member.  For a small environment that would be fine to just have the two switches.  
How do I configure 2 stacked Cisco 2960s Switches for use with an iSCSI Equallogic PS 4000XV?
Configuring 2 stacked Cisco 2960s Switches for use with an iSCSI Equallogic PS 
4000XV