Why would anyone want 180g records ?

DJs like the 180g records; they're heavier, and have a better feel for spinning and scratching.

In the original days of vinyl (aka records or LPs), audiophile recordings were pressed on 180g virgin vinyl rather than the common 120 to 140 gram. It's my understanding that creating a thicker record with deeper grooves could hold more information.

Nowadays, identifying a record as "180 gram" is a marketing term; if it's thicker, it must sound better.
A good sounding vinyl pressing comes from good mastering, an expert record cutter and technicians, and well maintained equipment. The actual vinyl disk could be 120g and have excellent sound.

Of course, some of today's pressings do have excellent SQ, my point is that it's not due to the vinyl being 180 or 200g. But that's what they've given us.
As far as advantages, one of the selling points is less likely to warp, even though some new records are leaving the record plants warped.

The weight can make a difference in helping the album to stay put without vibration.  How many of us use clamps or weights to help connect the vinyl to the platter?  Many times the 180 gram records are recorded better.  I love them-just my 2 cents.

200g is even better.

Here is a nice discussion of vinyl weight for LPs and whether it matters:
http://blog.vinylgourmet.com/2015/10/180-gram-vinyl-what-are-the-benefits-heavyweight-vinyl-records-...
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In general I like 180 and 200g records better, but I've also found that using a record grip (I use a KAB) helps make light records (e.g., 70g Dynaflex) sound more like 140-180g records. Each weight has a different amount of damping and a different resonant frequency. Try a record grip; you'd be surprised at how much it helps all records have a similar tonal balance and noise floor.