There are a couple of important points to consider when using Flowtables. Depending on the traffic characteristics, Flowtables may also drop the network performance. It also depends on the amount of rules and their configuration. For example, if we had much much more rules in nftables file for so many different operations (think of it like adding a new rule per IP address), Flowtables would hurt the performance in Ubicloud. They go hand in hand with how the overall network is configured. In our case at Ubicloud, it helps us, but we have a fairly simple Nftables definition as you can see a big part of it here https://github.com/ubicloud/ubicloud/blob/main/prog/vnet/upd...

I think history is at least a part of this. The software flow table implementation (which ubicloud demonstrates here, full disclosure, I work there) offers some speedup, but the motive appears closely coupled with hardware flow table offloading: https://lwn.net/Articles/738214/

nftables is very flexible and flowtables won't work (transparently) in all configurations.

For example sending packets from a single connection over multiple links round-robin. The cache will remember only one link and route all packets over that link.

And packets in offloaded connections will bypass nftables rate/bandwidth limits and counters.