This subject was covered quite recently by "Inna" and questions answered effectively in this thread :
As an aside I recently took receipt of a new LP which was advertised as "80g" weight. I naturally assumed this was a misprint and it was the usual 180g.
When I opened it the package was so light that I commented to my wife that it felt like they'd forgotten to insert the disc(!)
It was of course a genuine 80g pressing, not 180g, but interestingly, if you blind-tested it, you would find it was as loud & dynamic as the loudest pressing you can think of in any heavier weight material. This confirms that there is uniformity to the depth of cut regardless of what weight vinyl is chosen. Ultimately, it is indeed the mastering & moulding process which defines the quality of the result.