For a long time QoS was rarely used on Check Point gateways due to a longstanding incompatibility with CoreXL that prevented the two from being used together. This limitation was lifted in version R77.10+. However enabling the QoS blade on an R80.10 or earlier gateway would definitely cause a sharp rise in CPU usage on a busy firewall due to required special handling on the Firewall Worker cores in the QXL path (which also precluded full acceleration of QoS'ed traffic by SecureXL); as such if you were just looking to do bandwidth limits my recommendation on R80.10 gateway and earlier was always to employ APCL Limit actions instead.
However in R80.20+ SecureXL now has the capability to perform QoS itself (the new "QoS inbound" and "QoS outbound" processing paths) so the CPU hit when enabling the QoS blade should be substantially reduced in R80.20+. I have not had a chance to see this new R80.20+ QoS capability in action at a customer site yet but it looks promising.
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