I just finished staining the quarter round for my floors and I want to know if it's necessary to apply polyurethane? I followed someone's advise to condition the wood before staining and I didn't see any difference between the conditioned wood and the wood that wasn't, so I'm trying to figure out if this is another unnecessary step. I was going to poly the t-molding since it gets a lot of traffic, but the quarter round will only have a vacuum occasionally brush against it.
Urethane is a sealer and durability layer. It keeps cleaning equipment and shoes from scuffing through the surface of the stained wood and degrading appearance. It also prevents liquids from soaking in and staining. Whether you do it is up to you, but I've never seen un-sealed wood installed as base trim.