Commonest use is for vegetable growing - the purpose is to reduce the acidity of the soil for certain crops because if the soil is too acidic, the crops won't do so well. Not generally necessary in the average garden for growing ornamentals, but if the soil is tested and found to be highly acidic and you want to grow non acid lovers, liming will reduce the acidity.
Also a component in compost making formulations such as Garotta, where its used as a 'sweetener' - highly acidic compost heaps smell 'orrible, lol!

On the ornamental front, many alpines--such as Arabis--and Mediterranean plants--such as lavenders--prefer a neutral to alkaline soil, which makes lime, especially in its coarser forms, useful. In acidic clays, lime is also used to improve the soil structure, since the calcium in it binds the clay particles into sand-sized clumps, improving the aeration.

thank you all very helpful KEV.

Oh yea, I'd forgotten about lime and clay - I usually use gypsum for that because the soil here is more or less neutral...

Same here, Bamboo--though our soil is very alkaline--but by pure chance, I remembered the other! : )

And just for interest the process is called flocculation.

the other thing its used for is to decay bodies quicker under patios generaly bye serial killers lol .

True, NP.
Now Chlorate of lime is used to hasten the decomposition of waste material. We used to pour the stuff into the 'toilets' we dug when camping.

with the odd drunk hippy know doubt owdboggy lol .

You're scarin' me, man!!

Heavens when I went camping and digging 'latrines' Hippies had not been invented. Boy's Brigade captains might have been dipped in them, but not long haired eco freaks.

lol i used to be a paranoid schitsofrenic but we are all right now lol . dont be scared he he he lol .

Too funny NP! Are you sure that you're not still being followed? What do the voices say? :)))

not with 6 dogs lol . they say you used to be a wearwolf but your alright nooooooOOOOOOOOOWWWWWWwwwwwwwwwoooooooooooOOOOOO(OOOOOoooooooo lol

LOL!!

or i used to be a parrot but im allright now im alright now im alright now im ...........................................

Are you sure about that?

thanks everyone very useful and informative thanks again Kev.

Your welcome