Standing Room Only (SRO) tickets are additional tickets available to purchase in suites.
When browsing suites, the number of tickets included in the price reflects the number of stadium-style seats located in the suite. Typically suites can accommodate more people than the number of seats which is why Standing Room Only (SRO) tickets are available to purchase.
The descriptions within the private suite listings note the number of SRO tickets available and the cost per ticket. You are not required to buy the SRO tickets if you don't plan on having more guests than the suite price includes.
You, the suite buyer, are the only person available to purchase SRO tickets. If the suite is sold as private, the SROs are not released to the public.