300 f/4L IS as other than a sports/wildlife lens

Wondering how useful and worth having in my kit, the 300 f/4L IS would be. About 90% of my photography is event/concert work and the rest is a mix of sports/and nature stuff(birds,critters). Planning on having the 70-200f/4L IS as my long zoom for mainly outdoor shots and "bright" stage shots.
Like what I see of the output from the 300L but not sure how much real use it would get, may be useful at an event to mount on a tripod and just take candids(sniper shots) as people come into range.

It might be handy if you cant get quite so close to the stage or something, or a big outdoor event, or for when you want a tighter shot of someone on stage..

And its actually an easy lens to handhold so a tripod wont be too necessary...

it would work good as a portrait lens however... and also for outdoor things, it works great for flowers and everything

I use mine for more close ups of flowers, dragon flies, etc than I do for wildlife. Makes a great lens for that. And as KenjiS stated, very hand holdable.

I'm not sure if an f4 lens is going to be all that useful to you when you are doing concert work. I used to shoot concerts for a daily newspaper from the pit in front of a stage and used an 85 f1.8 (full frame) at ei 1600 and got shutterspeeds in the 1/500 second range. The IS will help with camera stability, but it does nothing for subject movement. SInce performers like to move around you'll need some shutterspeed.

If you can get closer I'd suggest the 135mm f2. If you can't then the 70-200 f2.8L might be a good choice. I have the non IS version of that lens and use it with a monopod - kind of do-it-yourself IS - but I'd use the IS version on a monopod anyway, and the 300 as well. They may well be hand holdable but I see no reason to use an unstable base as my arms tire, just to prove that I can or can't hold the thing steady.

Finally with the 70-200 f2.8 you could add a 1.4 converter. That'll take the 200 to 320mm and you are back to f4, but hopefully for other things. I'm guessing that the price of the 70-200 f2.8L (non IS) with the 1.4X is going to be about the same as the 300 f4 and the 70-200 f4L IS, and in my opinion the 2.8 version is a MUCH better buy. IS gets you platform stability, but so does a monopod; while but aperture gives you that shutterspeed to stop movement.