Tetra ethyl lead did indeed leave deposits when burned and those deposits had the surprising effect of reducing exhaust valve and seat wear. Valve jobs were routine up through the 1950s, but became much less common after that when TEL was being added to most fuel. It is true that TEL was added in order to raise octane ratings and thus support higher compression ratios, but the exhaust valve life improvement was a very real side effect.
When TEL was pulled away in the 80s it was a problem for some of the older engines which lacked hardened exhaust valve seat inserts. Now it is common practice to add those seats when rebuilding older engines in which the valve contacted directly onto the cast iron head surface.
John