I am a very new player and started out playing very loose and passive 42/6 until I got PT3 and realised how badly I was playing. At that point I was winning a small amount 5BB/100 or so I think (but a very small sample). After getting advice from this forum I started to play much tighter 19/14 and won much more and my winrate improved too.
I play 4NL though and think that playing very tight will mean winning but against the typical player at this level, it will mean missed opportunities. I recently loosened up (bad I know!) although still playing quite aggressively 24/20 and my winrate has increased even more. So many players at my level don't pay any attention to other people's hands only their own and seem incapable of folding so when I am sure I have the nuts I go all-in and almost every time I am called.
I should probably tighten up before I get into bad habits again but playing looser against villains who go all-in with top pair and ignore that you might have trips, a straight or even a flush is irresistible!