Naruto Verse
Rain is a element which is created using the mastery over water and wind element, Rain release in my opinion is one of the strong and as well as dead element of our RP, Strong because it is very versatile in terms of usage because you can use it too attack, defense, supplementary stuffs like the sticky rain stuff and my personal favorite to induce genjutsu and it is not all that makes Rain release a strong element, In my opinion it is rather tricky to deal with it too, tell me who is always looking up towards the sky while suspecting a attack instead of dealing with the opponent who is in front of him?
There are still couple of things which makes rain a very strong element-
1. It is fast in terms of speed.
2. In most of the cases it effects multiple enemies thanks to it's long range.
3. In most of the cases you can use it any where on battle field because when rain is pouring down, it poring down equally everywhere. etc etc.
Now I come to the second part of my statement and that being that it is a dead element, now I know it has a few disadvantages associated with it like, one need's to either have ongoing rain or summon rain clouds for using most of the jutsu which in does require good preparatory time, It is hard to use it in dry places as there is less moisture in the air and it can't be exploited easily and thus technique take's a little longer than usual time to be ready but still I think if we put aside these couple of disadvantage there is no main disadvantage associated to it where as the advantage are as much as you can come up with, but still people don't use rain element everyone want's Sound release now a days, I have a habit of reading Spar's and fights and I won't lie to you the last time I saw anyone using rain was like 6-7 months ago, The user was Xanthe and he had used the Stop Rain technique to stop his opponent's rain tiger will technique and let me tell you it was not a 1vs1 fight, it was a village invasion therefor it became necessary to stop that technique.
Real Life
Rain is nothing more than water which had once risen up from the ground as moisture, which was created due to evaporation, once the moisture went high up in the atmosphere it got condensed and fall back onto earth in form of rain droplet's, Rain is very useful to us as not only it provides plant's and trees with water but it also is one of the main source of fresh water for human consumption.