Smith will officially become a Leeds player when his contract at Oldham expires on July 1 after putting pen to paper on a two-year deal at Elland Road.
The 24-year-old, who scored twice in Oldham's FA Cup win over Liverpool last season and headed a stoppage-time equaliser in the following round against Everton before the Latics lost the replay, is 6ft 6in tall.
McDermott told the club's official website: "It is a major asset. But it doesn't mean to say we'll be smashing long balls in. He can take it in, hold it up, you saw his goal against Everton from a set-play.
"His movement is good. He's a work in progress, but he's not an 18-year-old work in progress. He's done well in games and we feel he is a good asset."
Birmingham-born Smith, who began his career at Cheltenham, played for Solihull Moors while gaining a degree in international management at Manchester University and was signed by Oldham in 2011.
"He knows the other side of life," added McDermott. "He's worked in different places and seen different things.
"It's very similar to Dave Kitson who we signed at Reading from Cambridge United. He'd worked in a different part of life before football.
"When I spoke to Matt - and it's very important to speak with players before you sign them - and looked into his eyes, you could see that when he comes into training every day he appreciates the environment he's in and what he does for a living."