Many LED light bulbs are not compatible with dimmers. if a non-dimmable light bulb is connected to a dimmer switch then it's likely to damage the light bulb. Even a dimmer switch set to maximum is not the same as a regular on/off switch, being turned on.
However, some LED light bulbs are dimmable, as long as you also use a suitable dimmer switch. It's important that a compatible dimmer is used, as an old dimmer that worked perfectly well with hundreds of watts of incandescent light probably won't work with LED lighting.
We recommend the Varilight V-Pro range of dimmers. These dimmers are also recommended by most lighting manufacturers as they tend to have the most compatibility with the largest variety of light bulbs.