It can be a tradeoff- one or the other. Do I have a glass of wine with dinner, a beer to relax after work, a drink at bedtime to speed up sleep onset? All very normal activities- and for some people there is no problem at all.
But for a significant number of us, including myself, even one or two drinks causes restless sleep, awakenings during the second half of the night, feeling tired or not really rested when we get up. That’s because alcohol affects brain cells in an early phase and a late phase (“phasic effect”). The initial calming and sedating effect of alcohol changes during the second half of the night, as alcohol is metabolized and produces a “release” effect on the sleep/wake switches in the brain. I think of this as a mini-withdrawal type of reaction which results in some activation and lighter sleep with changes in sleep architecture.
The bottom line: for a significant number of people, a drink or two in the evening leads to dissatisfaction with the quality of sleep: they awaken more easily, sleep restlessly during the second half of the night, and don’t have that positive sense of restedness in the morning. If you think you may be in this category, experiment with yourself and reduce or eliminate alcohol for a week and see what happens with your sleep.