What I think he means:
1- nobody likes huge maps, long walking times to get to fight. Unfortunately everybody always complains walk times are too long. Best thing to do is to walk out sections of Valve maps which are proven to work pretty good, do it with a standard class like pyro that has an average speed and can't jump/shortcut.
20 seconds is about the time it takes for people to get grumpy and it's usually only payload Valve maps that can be longer (off top of my head). But then you get a dispenser and better chance to survive for awhile.
2-transitioning is areas between points. paths need to curve to give cover and be interesting, and to help optimize your map. But mazes are not fun. Put a couple 90 degree corners in, not 180's. The players skill points should go towards fighting, not navigating tunnels.
For instance, if you go through a door that leads to stairs, you should be able to take a pretty straight path from door to stairs. Not turn right, go backwards, get on stairs, turn left, go foward. Just a nice smooth flow.
3- large spawn rooms that take 20 seconds to get out of. Same as #2 really. It should be a pretty straight path straight out the door.
An example I noticed a few days ago, in Hoodoo you go out of spawn, take a tight jig around a dumptruck, stumble on a hole in floor and then deal with enemy. Adding the jig around dumptruck and uneven floor just makes it hard and breaks the flow.
In Egypt you have 20 seconds of tunnels to get to spawn door in one of the stages. It's dark and confusing. Poor spawn room design is not clever, it's annoying.
Badwater has a few exits from tunnel for Blu (1st stage), but it only takes 3-4 seconds to get but and the tunnel is 'cover' to stop spam. It's not excessively big/twisty...