[xwiki-users] How end user can capitalize on groovy/velocity fscript in xwiki?

Hi all, i have seen xwiki can do lot of stuff with groovy and velocity.I am new to groovy so trying to understand how groovy and velocty can benefit xwiki and ultimately end user. As most of the site says groovy and java are almost similar. so why xwiki is using groovy when it built upon java. As per my understanding xwiki is using groovy as scripting language where admin can write groovy scripts at run time from UI which needs not nto be compiled but work like in the similar fashion to java. Internally we are passing this grrovy script as string to server which is compilinh it and executing it at run time. Right? Now second part is why velocity in xwiki? Velocity is used in similar fashin to groovy in xwiki but difference is that any user without programming rights also can write velocity scripts as it has access to limited set of apis . Apart from that we can also write front end in velocity script like if i write {velocity}Hello:$xContext.getUser(){velocity} it will simply say Hello:Scott on UI but inside groovy scriplets everything will be taken as java code. Right?