Hi ,
The command " no ip igmp snooping tcn flood" command is used to disable multicast flooding when there is a spanning tree topology change notification from the root switch. When topology changes happen, multicast traffic will be flooded to all ports for a period of time before it stabilizes. As stated in the document attached below: "Only the multicast groups that have been joined by a port are sent to that port, even during a topology change."
There is a possibility it's currently set on ports that receive and send multicast traffic. I would suggest validating the traffic path for multicast in your network to better understand which ports need the command.
Refer to this documentation below which expands more on this behavior :
https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/12-2/53SG/configuration/config/multi.html#wp1049520
"Some vlans also have pim sparse mode set."
- Vlans with this command set indicates that there are clients in those vlans that utilize multicast traffic. This is a PIM mode that is typically used when we have clients spread throughout the network and it uses a rendezvous point AKA "RP" which serves as the "middle-man" between the multicast source and the clients that need multicast traffic. This helps with limiting the amount of multicast streams sent through the network so yes, it's useful in limiting congestion on the network.
Please refer to this document below which expands more on this:
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti_pim/configuration/xe-16/imc-pim-xe-16-book/imc-basic-cfg.html#GUID-08C0EDBD-4A85-4FC3-AF2C-AA930C578F3C
