QoS will allow you to prioritise and rate limit traffic based on packet type, i.e. prioritise traffic from one switch port over traffic from another, or prioritise VoIP traffic over HTTP traffic. I'm not too sure what the capabilities of Linksys switches are in terms of the featureset, I'd imagine it can't do very much.
As a rule it's not good to play with QoS and rate limiting unless you have a great understanding of it since you can easily cause packetloss and slowdowns through improper configuration.
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is there any other good way to control bandwidth than QOS
You can try to rate limit their port with the Linksys switch, but if their moving any sizable amount of bandwidth the switch will probably freeze up. If this is for commercial (not in your home) purposes, you may want to upgrade to an older Catalyst (Cisco 2950 or something).