you need fast x sync more outdoors than indoors, indoors the ambient is controllable unless its coming in through the windows (in which case you can close the curtains) but outdoors you cannot control the ambient directly, but you can control it with the shutter speed which only affects the ambient and not the flash exposure, this is a very powerfull situation where you control 2 exposures in 1 image and and choose to, say, if you are taking a picture of someone, to let the background be 1 stop darker than the person, or 3 stops if you so choose, brighter if you want high key.
once you are at your highest x sync then your only option is to do a power battle with the sun by reducing iso and increasing aperture and flash output power, often if you are using a hotshoe flash then you will be loosing this battle.
the people who say flash ruins a photograph, I have been there too, but the truth is if it does then you are not using it correctly. homework for you guys is to read strobist