Lockout transfers support from primarily muscles to primarily skeleton.
There is more muscle tension shy of lock out, but there is more force required to pull a lever to full lockout.
Use both techniques if you're worried.
Dec 2013: 365 SQ, 275 BP and 415 DL.
Dec 2014: 500 SQ, 350 BP and 550 DL.
"Trust the process" - Steve Shaw, MaB Founder