Yes, the signal degrades more with longer cables which reduces the usable bandwidth. Short cables up to about 0.5m (1.5 feet) can use the full 40 Gbps. Slightly longer cables up to 1m can still carry enough signal for Thunderbolt 3 but usually at reduced speeds (20 Gbps).
Above about 1m (3 feet) a passive cable usually isn't good enough for TB3 connections and you have to use a more expensive "active" cable. Active cables have built in signal-boosting circuits -- they're amplifying and re-transmitting signals, not just passing them over the wires.
Above about 1m (3 feet) a passive cable usually isn't good enough for TB3 connections and you have to use a more expensive "active" cable. Active cables have built in signal-boosting circuits -- they're amplifying and re-transmitting signals, not just passing them over the wires.