Out-of-seat climbing

As a bike strength exercise, standing hill repeats are hard to beat.  Many benefits, and you should do it.

I incorporate a lot of standing hill climbs in my training. I have a route that includes about 1000' of climbing over 2 miles, including a 3/4 mile 10% grade and a slight downhill before another 10% grade. I start training that climb by alternating sitting and standing, gradually increasing the standing until I am climbing both hills and sitting the downhill. Then I reach the point where I can do 2x, then 3x, and by IM day I've been able to do 6x repeats on that route.  I usually climb at about 65 rpm on an 28 rear cog, about 300 watts.

Training hill repeats makes hillier IM courses seem like no problem. And I can easily pop up out of the saddle to top a ridge or accelerate out of a turn. Hill repeats have really halped me become a stronger, more well rounded cyclist and IM.  Yes, hours of hours of aero are helpful too.

As I say to my daughter, the only way to get better at hills is ride more hills.

standing allows you to generate more torque. If you want to drop people or attack it is a useful tool to have. training to stand comfortably for 20 minutes, a position where you are creating a ton of drag, is likely not beneficial for a triathlon. However, if you were contesting bike races with mountain climbs, it could be a skill to consider.  Also to note, we aren't pro's, and that is kind of weird even for a pro.

Training at different power ranges and cadences will make you a better all around cyclist that should translate to all types of riding.  I don't know if it's necessary to work yourself all the way up to 20' sustained out of the saddle efforts...but it's up to you.  Bike training is bike training in my book.  So long as your comfortable holding the aero position and putting down sustained power, then I don't see any problem with focusing on out of the saddle efforts...or any other types of training that results in the desired training stress.

Now if you are having trouble putting down sustained power while aero...then obviously you probably want to spend your time more appropriately.  

When I was doing a lot of spin classes, there was another "real" cyclist in the class and we'd often challenge each other to different workouts. One of the things we did on occasion was to take the saddle off and do the whole class standing. Yeah, masochistic and all that.