Potential Downsides:
1. Wasting time chasing women of short-term value instead of improving yourself, dating higher quality women, and/or focusing on vetting Mother of My Children candidates.
HOWEVER, the paradox is that you need to bang some short-term value women to recognize the GOOD women. The downside is when you don't realize or accept you have learned enough from gaming lower quality women and using that knowledge to go after better quality women that have potential long-term value. Some guys can get in a rut of just chasing a nut for the sake of the nut above all else; without any greater purpose or objective or maintaining any real standard about where they are getting the nut from.
When you're new to game, it's part of developing yourself and game training; to chase and bang short-term valued women. When you're experienced, it's like eating fast food when you know better. Once in a while it might be forgivable but all the time? Forget it. Better to just avoid it all together though.
Personally, I made a significant shift in mentality once I got to a certain level of experience; where I focused on fewer bangs but of much better quality. I pretty much turn down fast food bangs now on general principle that they bring little value beyond getting a nut along with significant risk. Speaking of risk...
2. Anxiety from banging high-risk chicks and the possibility of accidentally knocking one up.
Your entire life can get derailed over one nut. Seen it happen plenty of times. Every chick you bang is a liability; be it accident babies, STDs, false accusations, or something else.
3. Potential jadedness and bitterness with women and life; feeling you could do better if you were in a better city/country and therefore, you miss opportunities in the present.
If you know you could get on plane right now and bang a woman 3 times more feminine and 4 points better looking with 1/4 the effort compared to your current location, it can potentially kill your drive. Realizing your world market value is a very healthy thing but can lead to miss opportunities in your current environment as well.
For example, I was just walking around yesterday a bit pissed at the world; dreaming of places like Bangkok, Brazil, and elsewhere. While walking into a shop, a solid 7 gave me this beaming smile and constant eye contact as I walked by. Because my attitude was shit in that moment, I missed a warm lead and opportunity. Where could have that led? Who knows now since I had my head in the sand at the time over bullshit.
4. Sense of social isolation from many other men.
Not that you want to associate with them heavily anyway but I've lost more than a handful of blue pill friends since becoming red pill and doing the player thing. Some find the lifestyle repulsive and some find it threatening to their ego. If not the ego, their GFs/wives certainly will find your presence a threat and make it a point to get you excommunicated from the social circle. Since blue pill man are generally bitches, they go along with this non-sense.
It
can be a bit heartbreaking in a way to lose "friends" you have known for a while over something as straight forward as being real about women and life.
Overview
Aside from #2, the aforementioned aren't really downsides in the strictest sense but more like growing pains to becoming a better man and mostly come down to attitude and mindset in dealing with properly.
#2 however is a VERY real risk though; especially if new to the player lifestyle and you don't know how to vet for women who are potentially high-risk for an accident baby (ex: 30+ women), an STD (ex: drug addicts or especially needle users or women who have banged needle users), and/or a false accusation (ex: libtards; especially American white woman libtards). EVERY woman you bang is a liability and naturally the more you bang without knowing what to look for, the higher the chance you hit a landmine. It only takes one landmine to kill you so if I were new to the player lifestyle, I would recommend above all else learning in-detail how to vet for high-risk women. There are numerous threads on the forum dedicated to these subjects.